Did nobody see that his first post says he is looking for Zombie games?
Alan Wake is a great thriller game, should somewhat fit that desire. Dead Rising 2 is pretty neat, but the controls are seriously clunky and unpolished. It doesn't usually become a problem, only if you get yourself into serious trouble (You're bound to do it once.)
I hear the new Call of Duty has a zombie mode that's kind of decent, but only a survival game, rather than having any real story behind it (It
is just an added feature, to be fair).
And Resident Evil 5 is easily the best zombie-themed game for story, provided you have a friend you can co-op with, otherwise you'll find the game
very frustrating as the Co-op AI is sub-par.
As for non-zombie games:
I'd suggest Halo too, if you're into the more casual shooters. It's easy to pick up (As is the nature of casual games), and there aren't really any hard parts that can't just be olved with a bigger gun. Personally, not my kinda game.
Mass Effect is a hit and miss kind of game, you either like it or you don't, imo. I personally foud it to just be KOTOR all over again with a new conversation system, but as evidenced here, a lot of people liked it, so...
Rainbow Six is a little more difficult, but the story is great, and the variety of weapons and character parts really helps make your character your own. Controls well, and I believe it still has a big-ish community online.
As for flight sims, Ace Combat is more traditional, where HAWX is pure flight-fantasy. The moves you can pull off are ridiculous and reminiscent of Battlestar.
Armored Core: For Answer is undoubtably the best mech game avaliable hands down. Learning curve isn't really brutal, but as you get into the higher difficulties, it becomes a lot harder to defeat NEXTs (A
lot. White Glint is a standard measurement of how well you'd do on the next higher difficulty level)
And of course, there's Lost Planet and its sequel. Both games are great, and the second definitely improves the controls and engine of the first. You
can get it on PC, but I'd only advise that if you had a wired 360 controller you can play with, as the mouse and keyboard simply makes the game a trainwreck.
And then there's Dead Space, which was just
AMAZING.There are plenty of games out on the system that if you have a HDTV you should be able to find one you like. They even have a 2d fighter released on it now (BlazBlue), for those who aren't content with Street Fighters lack of technical abilities and all the complicated things. And Sonic 4. You can browse around the xbox site for the Live Arcade lists, far too many games on there to even mention.