There is so much to love about the game Dungeon Keeper. Despite the dated graphics the game is very playable and the mechanics are so good that the game feels it has aged incredibly well. Nostalgia aside there is something inherently fantastic about strategy games with perfect mechanics (well great mechanics at least. Perfect may be a stretch) where it achieves a zen no other genre can hope to attain.
The intro cinematic also will forever be hugely nostalgic for me (despite having aged considerably worse than the game).
What I really loved and continue to love about this game and the 90's on the PC in general is that true innovation was possible. Development costs were in line enough where developers and artists could really experiment and make whatever they want and chances are they would even break even.
It's also nice to play something that isn't The Witcher 2 or Minecraft. Why did Notch have to put Nether in SMP. Dammit.