Grimrock

I'd love to see a random dungeon generator, or maybe even an endless dungeon generator where your keep going down levels until you had enough or your party is in too bad of a shape.
Blizzard did it in Diablo, and since the game is essentially 2d as well (height has no meaning gameplay-wise), they might be able to use a similar algorithm for generating random dungeons levels.
This will give the game a lot more replayability.