I acquired a full Dungeon Saga Kickstarter edition plus all expansions and several add-ons (by Mantic games). The whole collections contains something like 140-150 figures

, most of which are fine for Heroquest. The sculpts are quite good, the plastic used slightly less so, it often warps during transport and you have to give them the hot water treatment to fix. But once they're in their proper pose, they're very nice (I haven't painted any yet, so I don't know how this type of plastic paints).
If you were to buy the retail versions, the base set has 26 figures, but while there are some nice house rule figures in there (zombie dwarfs, zombie trolls, Mortibris the Necromancer, and possibly the heroes), the minions/monsters are undead - skeletons (including archers) and zombies (including armored zombies). Their style doesn't really suit the HQ figures, although it would be fairly easy to just use the Dungeon Saga figures only.
The board sections could be used for custom dungeons I guess, I'm not too fond of the artwork myself - a bit too cluttered - but unlike most other dungeon crawlers, DS also has plastic 3D furniture, a different but mostly similar set to HQ, that can be used just fine together with the existing furniture (although it's fully plastic, so they would need to be painted - but then they would look even better than the HQ furniture). There are also plastic doors, including double doors and portcullises, though no "open" versions.
There are also two expansions that are worthwhile for the miniatures. Again, the figures are about the same size as HQ, but clearly of a different style, and the same goes for the board sections:
-- Warlord of Galahir focuses on Greenskins: Goblin warriors and archers, Orc warriors, archers and tougher versions, Trolls, Orcling (Snotling) bases, and a nice Orc warlord; 10 different sculpts in all, 19 figures total.
-- Infernal Crypt focuses on demons/hellish creatures, with various smaller and larger demons, including succubi and Molochs (ogre-sized brutes), and a nice demonic boss; 10 different sculpts in all, 19 figures total.
For either set as well as the base set, you can buy a set of figures separately, but those sets include half of what you get in the expansion, and do NOT include the bosses. The expansions are therefore a much better deal, even without taking into account the board sections and other counters.
For those who really like the figure style and want to expand their HQ bestiary, in their Kings of War line, where some of the Dungeon Saga figures also came from, they have figures for pretty much all of GW's races, so you can easily replace all official HQ figures and add lots of new ones, and for much cheaper than GW.