Like Rezfon said, don't get Fable 2, it will disappoint if you've listened to anything Molyneux said.
Oblivion is a good game, open world, lots to do.
Fallout 3 is like Oblivion, beautiful open world and pretty addictive. There's less to do but really is a damn good game.
Gears 2 has some great multiplayer, and the story isn't half bad. It'll get annoying sometimes if you're used to Marcus and Dom's personalities from the original.