Assassin's Creed - Fairly long game, especially if collecting flags is your thing. I personally really enjoy it, but it is a bit repetitive. The combat system and free-running feature really make it a lot of fun to play, at least in my opinion. Great game while listening to podcasts, too.
Gears of War - Pretty good online, but expect to get destroyed. Story mode is pretty nice, and a lot of fun when playing co-op with a friend. Also features online co-op and works very well.
Stranglehold - I've only played the demo, but it was pretty fun. Lots of shooting and context-sensitive stuff. Not as good as the others, but fun, mindless blasting.
Kane & Lynch - I played the demo and really wasn't impressed. I heard online is rather lackluster as well. I would rate this below Stranglehold.
Grand Theft Auto IV - Get this ****ing game.
Ace Combat 6 - Very sweet action flight-'sim', pretty good online too. Get it if you like blowing **** up with missiles, and shiny planes. But don't buy the expansion planes, they're ridiculously overpriced.
Mass Effect - VERY long, very good RPG. Huge ton of side quests, customizeability etc. Get it if you love epic sci-fi games, but prepare yourself to do lots and lots of riding around on barren planets in your silly little vehicle that can't do anything except shoot either its machine gun or its cannon. Oh, and it hovers. As you can tell, the Mako parts aren't my favorite thing, but everything else is pretty much awesome. Oh, and it has a few technical issues on the graphical sides, such as texture pop-in and long ass load times. And ****ing slow ass elevators.
Devil May Cry 4 - Awesome action game. If you liked DMC3, you'll probably like this.
I would personally also recommend Tomb Raider: Anniversary. Even if you didn't like the original Tomb Raider games, Anniversary is really great. It plays very fluidly and the puzzles are awesome.
Project Sylpheed is a lot of fun too, IMO. It's a great space sci-fi action game, it's a bit like Freelancer on crack and without any trading.
Um. Oh, Skate is great fun too. Beats Tony Hawk's ass a thousand times over. If you like skating games, or even if you're not a fan but feel like you might, give Skate a try. At least the demo. I'm not a skating fan, but the controls are so fluid and spot-on that I love the game to death.
