I am suprised DirtyBomb wasn't mentioned yet. It's a fantastic class-based Free-to-Play FPS which can be best described as a middleman between Quake and Counter-Strike in it's playstyle. It's also not Pay-to-Win, so everybody (even free players) have a fair chance against the people who buy stuff.
If you are into FPS Games it does not hurt to give it a try, as it's free-to-play anyway.
If you are into FPS Games it does not hurt to give it a try, as it's free-to-play anyway.