It's a game, it's simple, so we change it when and where we want. Someone wants the crossbow to be a two handed weapon, boom. Someone wants shields to work with two handed weapons, boom.
I admit it, like so many others, I nerf the HeroQuest crossbow. According to Avalon Hill it's always been intended to work like this:
Crossbow has unlimited supply of arrows. Whether wielded by a hero or crossbowman mercenary/evil crossbowman (or, theoretically, an elven mercenary of any type): It doesn't interfere with any weapons or armor, and it can hit any square you can "see" (meaning trace an unobstructed straight line from any part of your square so that it touches another character's square without intersecting the square of another character or closed door along the way), and yes it can shoot straight through tall solid furniture IF ZARGON WISHES (or if he wants it the opposite way, it can't, see the First Light rulebook). It just can't shoot through closed doors, walls, or through one character to hit another on the other side. It can't shoot the four adjacent cardinal direction squares touching the crossbow wielder, but it CAN hit the four close diagonals. And of course it can hit all the squares outward from it as long as (see the restrictions on objects in the way). It can't be wielded by the Wizard (or Warlock or Berserker).
My restriction is that it can't hit those four close diagonal squares (so the ten
[oops, I meant "eight" sorry] squares surrounding the figure are prohibited for firing). Otherwise it's the same as AH's interpretation for me.
I don't adjust the price, or add carrying capacity restrictions. I still allow unlimited arrows (no upkeep costs), no "string break" mechanics, still unlimited range. If you have a spell or potion that boosts your attack dice, it works for attacks made with the Crossbow as well. You can pass it to an adjacent ally just like any other item (or if you die, they can pick it up where you dropped it). Everyone in the party can buy one between quests (though a few characters can't use it). Having two crossbows doesn't change anything (no special dual wielding rules, see the Rogue for the only exception). But Heroic Brew? Two shots with the crossbow, against the same (or different) targets as a single action. "Twist wood" spell destroys it, as does the Wizards of Morcar version of "Rust" (while GS "Rust" can't since it's not a "metal helmet/sword"). An Ice Gremlin can steal it, so long as it isn't the weapon you're wielding (meaning you used another weapon on your last turn).
If things are getting too easy from crossbows, I start introducing monsters with ranged (and diagonal) weapons of their own, which is also built into the game.
For me "cannot be combined with a shield" is a handicap built into the game to force a tradeoff for two weapons: the Battle Axe (because it's so powerful) and the Staff (because it's diagonal). The latter some might have a problem with, because the Wizard can't use the Shield so why bother (not that only the Wizard can use the staff but it's one of the few pieces of gear he can use)? Plus, even in the EU editions the Staff isn't the only diagonal weapon (Spear, plus Shortsword in all but the very earliest printings)... and in the NA edition the Longsword is diagonal (no Spear and Shortsword loses diagonal ability, plus Staff is nerfed to 1 die). Of course with AH's rules you don't need a staff to hit diagonally, since the Crossbow can do that already.
To me, the issue is more that it's not spelled out how you're supposed to not combine the Battleaxe/staff with the Shield. You can't have the benefit of them both at the same time, yes, but you could read it as if you have both, you have to discard one, to have the other even in your possession. But to me the "switch at the start of your turn" (no action required) is fine and easy solution, and you don't get to switch back at the end of your turn again (or else you could always be defending with the shield and always attacking with the staff/battleaxe).
Many others have proposed that switching weapons takes your turn's action (but there are many instances where you would want to not do that... here we're imposing a penalty to prevent someone "cheating" while when you lose a weapon for any reason, or gain one, you want to switch immediately; imagine if you searched for treasure and found one, now you can't even equip it until your next turn!). I don't think the system is broken as it is, just not everyone can quite agree on what part(s) they don't like and if they do, the solution, and that's fine.
I mean, to me the hitting of the close diagonal squares almost feels like cheating (vs. the game's rules, not against realism/plausibility), but it's allowed. I'm sure there are people who play it "as written" who just allow you to switch stuff around so the shield w/ BattleAxe/Staff thing is effectively no restriction. So long as the player always remembers to tell target he switched at the beginning (and end) of his turn, then that's that!
