This free game called zombie panic: source is my favorite game ever. It's a mod for HL2 so if you have a source engine game you can play it. You start as human and you try to survive and do objectives. No NPC or AI int his game so it's all humans which makes it funner IMO. Download it here http://store.steampowered.com/app/17500/
Just press the / key to stop the game mp3 playing and then you can listen to trance and play this game.