I do notice a lack of any of the big shooters on your list. Personally speaking, I like Halo: Reach, but there are those who strongly prefer Modern Warfare 2. It's not my cup of tea, but hey, to each their own, right? If you're playing offline these might not be worth your time, but if you've got xbox live (and you should, personally speaking, I think it's the best part of having an xbox) then these games have some of the core xbox experiences.
The Fallout games are good, if you like Oblivion they've got a fair amount in common in as far as what makes the gameplay fun (though personally speaking I still like Oblivion better).
Finally, if you've got xbox live and some friends who want to play it with you, or someone at home who'll want to play local with you, Borderlands is a lot of fun. I think that it'd kind of suck if you were playing it by yourself, but when you've got a couple of your friends, and you're running around having a good time in the game, well, it's worth it.
Also, if you get xbox live, you can add a Netflix subscription on top of it and stream stuff through your TV, I ultimately canceled my cable because of this, and Netflix sees more use than anything else on my xbox, so even though it's not a game, I'll suggest that too.