Alan Wake
Metro 2033
Forza 3
Mass Effect
Those are the ones I really recommend. Although Halo:Reach actually sort of surprised me. It was pretty damn good.
This. I agree with others they posted. But I just finished metro 2033 again. Its an amazing game. Atmosphere is the best I have ever seen in a game. Great story, great gameplay
Don't bother with Fable 3. It's terrible. I'm not just Fable bashing - I may well be the biggest fan of the first two games you'll actually find on this forum. Fable 3 was rushed. It's a mess of several half baked ideas pulled together under genuinely the worst written story I have ever experienced in a "triple A" title. It's also the only game in the franchise that designates your player character with an alignment - good guy. If you want to be evil the whole experience will feel very inconsistent what with you slaughtering villagers one second and then promising to reopen their university the next. Get Fable 2. Its cartoony aesthetics are far nicer than its successor's bland hues of grey, which means that the graphics still hold up, and literally everything else about it is superior.
Anyway.
Alan Wake and the Halo games (get 3 and Reach. 3 is a bargain and Reach has some of the best multiplayer on the console. ODST should be boycotted out of principle (and it's pretty bad anyway)) are the only 360 exclusives aside from Fable 2 that I think are worth it. Mass Effect is a Microsoft exclusive and in some ways it's better than ME2 (depends whether you like RPG or action elements more). Fallout 3 is technically superior on the 360 - the PS3 version is pretty buggy.
Frankly there's not much left in the way of exclusives for the Xbox. If I were buying now I'd go with the PS3 (and this coming from one who only owns the 360).
I loved fable (tlc), after that it just wennt downhill. 2 I despised, I am bitter about it though becuase I loved fable 1 and was dissapointed. 3 on the other hand, uh its just bad. I set my expectations at 2 and just hoped for that at worst, hope they learned from thier mistake. But no, it was just terrible. Now its a kinnect game. Also I know your from the LH forums, did you know some devs left, that suprised me, I think fable isnt just being dragged down, but its dragiing LH down with it.
I still need to get Alan wake, but it looks good.
Buy reach its a good game. Halo 3 is great too, apparently still has a communit, so I need to buy it back, but the SP was great.