I have played Gunz the most for free FPS's its great. The strafing and running/jumping walls add a ton of gameplay and skill to the game. It's the best free FPS I've come across. Now I'm set on warrock as it also has a good player base… its free to download, you just need to download it and create a free account. Even though warrock premium users have more power over non premium users, the game is still pretty good and fun.
I didn't make it!
My favorite First person Shooting games are here like : Counter Strike, Medal of honor, Call of Duty, Battlefield series, Half0Life Series, Doom Series, Duke Nukem, Splinter Cell, Metal Gear solid, Hitman, Ghost Recon Series and many more.