First a list of issues then a list of fixes:
The main issues with BQP as printed in 1992:
1) quests one through three are intended not only for a "solo barbarian" and an 'unequipped' one at that, but even for a player brand new to hero quest. We know the "age 14 and up" is solely because of lack of safety testing ("pointy swords" as they would have said back in 1989) not because they don't intend 9 and 10 year olds to be able to face the challenge in this quests. Because of extreme difficulty like facing a YETI that can kill you with no recourse (if he does any damage, you get "hugged" and there is no mechanic to escape when you're alone, so you will die within four turns). A seasoned player who is fully equipped (4 attack/5 defense at least) has a chance to survive IF he doesn't run into the Yeti (the Elf player in his solo set isn't quite so lucky). The quest book explicitly says you don't get to hire mercenaries. A way to make this easier would be to allow you to rescue prisoners that serve the same function along the way (for instance in the default series an enemy crossbowman surrenders his weapon to you in exchange for his life and then runs away, why not have him fight by your side as a fully controllable character?). According to the rules of the original, despite there now being a new miniature for the "female barbarian" (with identical stats to the default male version) she CANNOT be used at the same time as the other barbarian as a hero in the same quest, so still four heroes max at a time (though the original six mercs would add another 12 body points to the group, now hiring 12 would add 24 body points which would be a big help making at least quests 4-10 more survivable). As before if a hero dies alone with no healing abilities to save him, he's out for good without the elixir of life and if no other hero or merc can claim his loot it is claimed by monsters and can't be recovered.
2) quests four through ten, while extremely difficult, at least ALLOW you to purchase mercenaries (assuming you have gold saved... and I guess in theory the "beginner" barbarian of quests 1-3 is now joining the "seasoned" Dwarf, Elf and Wizard who already have many more quests under their belt and potentially all the gold they haven't squandered from the GS and possibly KK or ROTWL but we can't assume they have any other expansions but this one). While the Heroes should be much better equipped by then, quests 9 and 10 are a "two parter" with no automatic healing and trips to the shops in between. IF the Barbarian survives these solo quests, he will have some good weapons and armor, for all the good they will do later on against the massive hordes you will face, far greater than any other quest pack. Increasing the gold rewards slightly (or stuffing those empty chests with some better loot) would go towards this goal of encouraging them to load up on mercs. Or buffing their abilities... or taking a hint from Wizards of Morcar and allowing the "retainer fee" for a surviving merc being at a discount. Wizards of Morcar also had a "potion of charm" that allowed the Heroes to implement a discount when hiring men-at-arms, that would be excellent here, and make it a Treasure deck card.
3) These mercs while useful in providing extra muscle (and the scouts, while weak, allow you another chance to search for and disarm traps like a Dwarf would, though if they fail to disarm they are almost guaranteed to die since many furniture traps do 2 BP damage anyway), will die quickly in most circumstances, as the monsters are big and powerful. Yetis can grab you in that hug (and essentially stop being useful at that point because someone else can walk up and hit it to kill it, releasing the hugged character, but a merc who is grabbed is dead in 1 turn). Ice Gremlins, despite looking like icy goblins, have 3 body points, like a Chaos Warrior. Yes, they can run away with certain of your gear and the rules don't explicitly state that it all is retrievable in the gear hoard room or whatever it is called, only what was captured on certain quests, but a generous Zargon could read between the lines and assume it is everything stolen up to that point. Polar Warbears get two attacks and it is not explicitly stated that the single defensive roll for these two attacks the hero is allowed can carryover into the second attack or if the second is completely unblockable with no defense though this seems the implication. The frozen horror himself has 12 chaos spells... I'm not against a game being challenging, mind you, but there are a few places where it really feels they are going for Total Party Kill especially in those early quests. Going into "shock" is the new way to render a "0 mind point" hero. Instead of either 1) going unconscious meaning he's dead unless the other heroes win and presumably drag his body to the stairs/door to escape and revive next time or 2) dead forever unless someone has the elixir of life to use on him that round... now the hero is reduce to one movement die, one defend and no attack. There are ways to increase mind points through potions but it doesn't explicitly say in the rules that a hero can come back FROM a state of shock once he's gotten there during the quest. And yes, there are more spells that allow the bad guys to reduce a hero's mind points to zero or one pretty quickly, which is also bad news for the Barbarian who normally only gets 2 (Talisman of Lore: 3). His artifact that boosts it by 1 permanently is not found until quest 7. And yes there are new treasure cards to expand that deck though some of them are bad for the heroes ("poison!"). There are also lots of icy rooms and ties that do extra damage unless certain artifacts are found and worn or certain potions used immediately. Yes, we now have traps that do unblockable damage if you land on them (stalactic traps) and undetectable traps (Wandering Monster traps though the monster's attack is defended against normally... the only undetectable unblockable trap in the previous packs was the giant rolling boulder from KK if I recall correctly).
As revealed by the early notes, ORIGINALLY there was a way to escape from the Yeti "hug" through a simple dice roll without needing another character to save you, making it survivable in solo quests. Clarify the rules so that the defensive roll DOES count for both Warbear attacks (or just make them two normal attacks meaning the second gets a full saving roll), allow stolen gear to be retrieved in full. Make it clear shock is "cured" by a return to positive mind points. Stalactite traps could be (rarely) jumped but also detected and disarmed in theory... except when they are in doorways. An unpublished planned rule in the draft notes indicates they were going to allow heroes to BLINDLY jump traps, meaning they could, if they suspect something on the other end of the doorway, roll for jumping and Zargon would allow it... THAT could make these instant hit, unavoidable traps more tolerable. Those are my suggestions if it isn't already too late (for all we know the books are already printed and just waiting for shipping and the "Q3" release date is just a scheduling thing). Then again look how fast they fixed errors in those "free" quests when fans pointed them out, and we even got live updates on those, so they COULD introduce some minor tweaks (even if they are "suggestions on how to improve this classic quest" at the end of the book via an "errata insert").
At least there are new Alchemist Shop spells, even if half of them are exclusive to the Barbarian. In theory as before there is no limit to the number you can buy, except your gold stash.
4) A few unmarked chests (not even "empty") this gives the game designers another loophole to make the game a bit more fair. Put something useful to the heroes in those chests rather than leaving them blank or making them explicitly "empty." The special artifact that boosts the Barbarian is not found until quest 7.
5) The Armband of Ice artifact is never found. Yes, it's just a stronger version of the "ring of warmth" but that affords another hero to get some defense from the many ice-related traps and spells out there that sap their strength. Yes, the heroes could be effectively immortal if they had infinite potions but they don't have infinite gold... this could be placed in some of those unmarked treasure chests, or anywhere, really. The Amulet of the North is given pretty late in the game (quest 7).
Little tweaks here and there like increasing the gold values could also help. More gold means more potions and (at least until they max them out) more mercs. You can cast spells on Mercs (and at least in one case they can give up a weapon to a hero; and if a hero dies, he can allow his mercs to continue to fight for him I guess and in theory keep his gear from being claimed by monsters as what normally happens if he dies alone), but nothing says they can use artifacts or drink potions, however.
Otherwise, sure, the Elf Quest pack has some even greater issues, even if the overall difficulty of that one is slightly less (especially at the end, the monster body points of those last two quests are far higher in the frozen horror).
Giving more potential mercs to buy is a step in the right direction even if it sounds like "pay to win" (but it's really not, this is fantasy money, not microtransactions!).
Hasbro/Avalon Hill... please fix the issues in Frozen Horror before release. Or failing that please do your dardest to inform all buyers of the EASY fixes to what is the second most broken and surely the most difficult HeroQuest set ever officially released due to sloppy editing, rushed production and clear lack of playtesting. Remember, very few players actually played these quests back in the day so they will have less nostalgia. What they are buying is an IDEA... that this was the "one that got away" by the time they placed their order or saw it was already removed from production (sounds like players who found out about the pledge drive too late or the Guardian Knights 2 days after pre-orders were announced).
If they include an "errata" with suggestions for improvement, that will satisfy me. Or if they want to have "difficulty levels" or "advanced mode" or something, where one is (broken) vanilla and the other is "tweaked to be comparable in difficulty to the earlier quests or at least not such a jump up" that's even better. Players can still get the 1992 quest book online and compare to see what it was originally, I suppose. Other than making the Frozen Horror an "it" we don't know what changes to the gameplay will be made. While before I was praying they didn't touch the mechanics for the GS/KK/ROTWL, now I'm asking for the opposite, because by default, the Frozen Horror BQP was "broken." Not all buyers are going to be hardcore fans of the internet community here to seek out the fixes and use the homebrew sander to buff out the rough edges.
Now some proposed fixes...
1) Discount for Merc retention (WOM it was 10 gold to retain each surviving Merc). Encourages heroes to not throw them away like cannon fodder, and able to buy more of them (we have twice as many mercs to buy now!).
2) Escape mechanic for Yeti hug attack. early draft notes indicate it was to do only 1 BP damage per round and the Barbarian has a chance immediately and on his future turns to roll 2 combat dice... single white shield means he avoids damage that round, 2 white dice means he breaks the hold. Yeti CAN defend from outside attacks while in the hold but does so with 1 die less.
3) Recovery from "Shock" state possible. Bring your Mind Points above zero and that character recovers.
4) Trapped treasure chest correction (solo quest #2) . Instead of a line of Spear Traps around the chest (letter "D"), the Treasure Chest itself has a spear trap on it that can deal 2 BP of damage to the Barbarian if not disarmed before searching for Treasure.
5) Treasure chest is NOT empty (solo quest #2). Treasure Chest (letter "B") actually contains something useful, like a Potion of Healing (restoring up to 4 lost BP).
6) Polar Warbear second attack defense clarification. The target of the Warbear's attack gets to roll their defense and if they block all skulls, any EXTRA white shields rolled are allowed to be counted against the SECOND Warbear attack (since they can always attack twice). If the Warbear monster strikes two different targets, each gets to defend normally against each attack. Or you could say that the Warbear does his two attacks against the single hero, then they get to roll their defense and the white shields count against BOTH attacks. Alternately the mechanic could simply be changed to say that while the monster gets two attacks every turn, the victims all get to defend each time as they would against any other attack.
6) Solo quest Merc "prisoner rescue" option. (solo) Quest 1: the Crossbowman (letter "B") immediately surrenders when the Barbarian tries to attack him. The hero then has the option to either A: let him go (taking his crossbow in exchange for his life) or B: press him into service (his life debt is repaid at the end of the quest, so he cannot be re-hired). This character functions exactly like a Crossbow Mercenary at full strength under the Barbarian's control for the remainder of the quest.
7) Armband of Ice reward for completing quest 3. The Village Elder Gothar was able to discover this artifact during his period of captivity and grants it to the Barbarian as a reward for his rescue.
8) Unmarked chest in Quest 9 assigned something. Considering the extreme difficulty of this quest and how heavily guarded it is it should be something really useful like the Elixir of Life artifact.
9) "Blind" Trap Jumping mechanic introduced. In the game system rules, jumping traps require that the location of a trap be first discovered by searching (or else known in the case of a visible sprung Pit Trap tile). A proposed rule in the draft stage was that a Hero (or Merc ally) could simply choose to jump a specific square. Only if they failed (rolled a Skull on 1 combat die) and landed on the square they were attempting to Jump would Zargon be required to reveal if there was a trap there, and the consequences. This would give Heroes a chance against "trap on the opposite side of an open door" incidences, especially Stalactite Traps that do instant unblockable damage, and Wandering Monster Traps which are otherwise undetectable. It would be sheer luck and guesswork on the part of the heroes and still has a chance to fail of course. Only downside is that paranoid players could be jumping the square every time, but since they can only jump one square, they will still guess wrongly and fall into some traps most likely or get lazy and caught off guard later. I notice that there are several instances of TWO squares in a row being trapped, not just the one in the doorway so it's as if they designed the quests with this mechanic in mind and forgot that they hadn't actually typed it into the quest book's rule clarification notes!
10) Ice Gremlins can steal your stuff and run away off the board with it. They are harder to kill than Goblins (having 3 body points!) so while there are certain quests where there is a tile that is the hoard of thievery that the Ice Gremlins have accumulated, it is not clarified that this is all the gear STOLEN SO FAR in the whole campaign or just in that particular quest. I think the opportunity to get some (or all) of your gear back if you are patient enough could be a nice boon to the heroes after all that difficulty as it is.
It's a short list but if the above were dealt with, the 10 quest campaign could be a lot more enjoyable while still retaining a decent amount of challenge even for the most seasoned of HeroQuest players.
Please feel free to add more... and share this list on Twitter with Avalon Hill and with new players who don't know!