The Halo series. (Including ODST)
Just... Halo... An epic war between a *mostly* ruined human civilization and a hyper religious, crusade like, alien brotherhood. A main character so manly it would make most 80's action stars blush. "I'm going to give the Covenant back their bomb."
Now for my reasoning for liking ODST. It was generally well rounded. I liked the characters, especially Mickey. I felt the plot was good, it was just long enough to not outstay its welcome. I do genially enjoy firefight. Plus my copy of Halo 3 was broken so it gave me a reason to pay for the game.