From what I have heard (though I haven't played it yet) Braid is amazing. That said, you can't go wrong with Geometry Wars. So either way you won't be disappointed.
World at War looks good, but then again it is made by the team that made Call of Duty 3 (though they didnt have long to develop it). I don't play online, and I enjoyed Halo 3. If CoD: WaW is only the same length for single player as CoD4 was, it will only be worth a rent.
Fable will get better and better, and the sequel is looking to do everything they aimed for (and missed) in Fable and then some. Thus far, I am yet to see a pessimistic preview of Fable 2. Obviously I am biased, but the title truly looks excellent. Then again, it depends what you are after. Given the way Fallout 3 has gone, I think Fable 2 will be the best WRPG of the year hands down. But if you are after a JPRG, you may want to look at Last Remnant (and DEFINITELY pick up Lost Odyssey cheap).
Most online heavy games come with 48 hours of free Xbox Live Gold to give you a trial. This will help you decide if Gold is something you need. (Apparently Fable 2 will have 48 hours free gold to try out the co-op 
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starcraft - Playing Games = FUN, Talking about Games = SERIOUS
