Yeah but you could use the render-engine of Unity 3 which is, i would say, fairly decent, more decent than the engine used in Achron anyway. Now lets just ignore the 1 million $ needed for assets to make any kind of AAA looking 3d-game nowadays..
But in the end you make the games you like and thats good.. ^^ AI War does at least not look ugly (anymore - lets not remember anything pre 1.0 ,p )
Point being, if you need a 3D-Engine to make that Dungeon Keeper Clone you have one ^^