I would highly recommend you Left 4 Dead. One of the best FPS this gen. Sure graphics are not as great as gears2 but this game is sooo much fun. Co-op on Xbox Live is awesome.
Fable2 is great. I really liked it. This is not a game to play at your friends house, because your character becomes kind of individual. So go ahead and play it for yourself. You will see how great the atmosphere is and how awesome the environment looks.
If you like Ninja Gaiden II, you should give Ninja Blade a try. Screenshots and movies look promising, don't know why japanese users didn't pick that up.
If you are into retro or creative games without a million dollar budget, you will LOVE Xbox Live Arcade. Braid / Castle Crashers / Uno / Geometry Wars(2) / Catan / Doom / Sonic etc. Some great games to download.
And of course Alan Wake looks more than promising. This seems to be a mixture of survival / action-adventure with a great story.
Forza 3 will be released this xmas. That's what the team for the menu said. I don't like racers at all (well except PURE, that was fun) but a lot of people are very positive about the Forza series. 4.36 million sales is a good indicator, even though it was bundled. So you should check this one if you are into racers.
Imagine not having GamePass on your console...
