Too Human, its a loothogs dream and violent as hell.
Frontlines:Fuel of War, before they updated it and removed certain abilities(mines on helis, mines on trucks etc) it was stupid fun, I would do suicide charges and kill tanks by slamming them with my jeep, or take out tanks with a little RC helicopter.
Halo: ODST, the story was better than Halo 3's in my opinion and I liked firefight more than any multiplayer mode before or since in the franchise, I LIKED feeling weaker than the enemy, its why I rarely play any Halo lower than Legendary.
Halo Wars: No it wasnt as deep as Ensembles other stuff, but it was the best I've seen on 360 and it was simple enough I even convinced nonRTS players to join me a few times.