I played Dungeon Keeper back in the day. It's a really good game. Not necessarily one of my favorites, but it's a really good game nonetheless. Unique, and very creative in a lot of ways. It's interesting how it reverses the roles: instead of leading an adventuring party into a dungeon, you are an evil overlord who has to protect the dungeon against adventuring parties. Lol... That alone caught my attention when I first played it. Very ingenious. Another thing that I always found interesting is how you could take control of one of your minions, a fly for example, and see the world through their eyes, in first person perspective. Kinda useless from a purely mechanical standpoint, but very intriguing nonetheless.
I think that my major criticism of the game (the first one, at least) is that there aren't really as many creatures as you would otherwise believe when you start playing. When I got my first flies, spiders and beetles, I remember thinking "oh, if there's three types of bugs (instead of just spiders, for example), then there's going to be a lot of different creatures for my dungeon!" But no, there's really not that many.