Also, if you get Oblivion, be prepared. Bring food and water that will last a week, a porta-potty/diapers, and ultraviolet rays so you don't get sick from lack of sun.

Still, Bioshock is the best shooter on the system single-player wise (that being said, it doesn't have multiplayer). I prefer Call of Duty 4 over Halo, but that's just me. Get both.

Gears of War, obviously. Mass Effect I guess... check it out first. Orange Box, great value and all of the games are great.

Oblivion is Good, But only if you know exactly what you are doing.
Its one of those games that you cant let go for hours on end. If you know what i mean..

I know people already said this, but Oblivion's a fantastic RPG for Xbox. GTA gets old incredibly fast in my opinion, and doesn't count as an RPG, obviously. If you really want to get with the RPGs, go buy yourself a secondhand PS2 and hit up the Final Fantasy series, because it doesn't get any better than that -- gameplay in 12 was fantastic.

The current game I'm addicted to on Xbox isn't an RPG at all, but a classic-feel platformer N+. Basically the physics engine in it is one of the best I've ever seen in such a stripped down game, and the level progression is perfect. The multiplayer is especially fun, but I have to confess playing it single player for about 2 hours.

Please, somebody tell me I'm not alone... such a fun game.