I would have to go with... Mount & Blade.
The community, while not small, is quite obscure. At least in my opinion... And I feel as though I am the only one who has EVER played it...
You can ride around, attack pirates, attack villages, attack castles, attack cities... You can attack pretty much anyone...
And the noises the weapons make when they bite into the flesh of those evil Nord bastards, wonderful!
Oh, and when you kill all the soldiers in a fortress/city, you can ask your king to give it to you! YAY!
The whole point of the game is to kill everyone... I think... It's still in it's beta, and you can only get up to level 6 without paying... And, in M&B, level 6 ain't gonna get you any where... But, at higher levels, it rocks!
Also, Sacrifice... Awesome game...