How could I forget to recommend that game?
+1 for correcting my mistake

Thank you for all the great suggestions so far! I'll be sure to check them out, watch a few videos on gameplay like you said and see what looks appealing.

For Dungeon Keeper like games I recommend:

*) War for the Overworld: Pretty much the same thing as Dungeon Keeper, just newer.

*) The Dungeons series: This series borrowed a lot from the Dungeon Keeper formula but also tried out some new things to change it up a bit. And not everyone likes the changes they made. Certainly not a bad series IMHO but not everybodies cup of tea. You might want to watch some let's plays to see if you like it.

When it comes to older games like Dungeon Keeper:

*) Startopia: I'm surprised no one mentioned this one yet. Sadly this game was removed from GOG about half a year ago but it is still available on Steam. This game mixes some elements from Dungeon Keeper and Theme Park and was made by the same people as those games. Highly recommended.

*) Evil Genius: Was already mentioned and I agree.

*) Ghost Master: Also a game you might want to look at. Though it is a bit different and you might want to have a look at some let's plays here as well since this game also isn't for everyone.

I think Majesty is kind of like DK. You don't have direct control of your heros so sometimes hilarity ensues.

Thank you all for the great tips!