What is a good FPS on the 360 - READ DETAILS!?

Do not recommend the obvious ones. I am fully aware of COD, GOW, GRAW, and Battlefield. I am looking for a game that doesn't have a hugely over-populated multiplayer member tally. I am sick of the COD games giving me unfair stats because of bad connection. I want something that is a solid shooter, not heavily populated, and is a fair game when played online. Also, if you can think of a cheaper game, that would help. I'm kinda broke lol.