The Elder Scrolls Oblivion is one of the best games out there in my opinion, if you like that kind of game. The new Turok game that's coming out looks awsome.
I've owned my xbox since sometime now. My favorite games are Call of duty 4 on Xbox live its one of the best games ever! Also assassin's creed its my top 2!
Get COD4 if you like halo. It's a lot of fun, same with Assassin's Creed. If you like music games, try Rock Band or Guitar Hero. and call support if your Xbox LIVE isn't working.