Don't buy Brutal Legend. Sure, it's a good game, but once you beat it that's it. There's seriously nothing else to do with it. And when you complete it, you won't want to play it anymore.
If you played Fallout 3, it might be worth the DLC, but don't buy a new disc for it. Just download a few off of the PSN or XBLA, namely Broken Steel and Point Lookout.
My choice out of all of those games is Demon's Souls. The game is amazing. It's really really hard, and you will die a lot, but you will keep coming back to it. It's basically a hack n slash game that requires you to block, dodge, etc. to stay alive. If you just go running in trying to kill everything, you will die within seconds. But if you take it slow, you can proceed. If you don't like hard games, then go Uncharted.