Overlord is pretty fun.
You basically capture the souls of those slain, and those souls are used to summon your minions from the netherworld. Fire creatures give you red souls, which you can use to summon "Reds" or fire minions, and so on and so forth with blue, green, brown. So it basically comes down to getting souls while doing quests to unlock the next set of quests, or areas. Your "Dark Tower" where you reside can be upgraded with things you find and loot. Including one of two mistresses, Rose or Velvet.
Your main weapon, and the focus of the game is of course the aforementioned minions, little scamp-like demons who follow you around in a pack and will basically destroy anything or anyone that you command them to. Besides carrying out your will with direct force, you can also sacrifice them by having them jump into your forge while you are creating weapons or armor, and they will imbue your creations with different qualities. The more you toss in, the more powerful the effect. My fire mace is unbelievable.
I have read people complaining that the overlord himself is weak, but I find myself at the front of the battle most times with my minions, laying out enemies left and right!
I think it's a great game, it's the first in quite a while that I have went so far as to finish. Almost. Ive got a couple more key battles and I'm done, but I'll prolly play thru again.