The title basically says it all. Like Dungeon Keeper the main focus of Evil Genius is on building a base, securing your income and recruiting minions while working on your plot to take over the world. Unlike Dungeon Keeper you don't need to spend as much effort keeping your minions content and trained as in Dungeon Keeper, as long as you setup some basic facilities they'll basically take care it themselves. Additionally you don't have as much control, you can't move your minions and you don't have any spells.
Overall though a very good game and a worthy spiritual successor to Dungeon Keeper