While not exactly a shooter I do recommend superhot
Screen cheat is an awesome first person multiplayer shooter where you cant see the other player's characters so you need to look through their screens to get a guess as to where they shoot.
And lastly, again not exactly a first person 'shooter' and more of a first person tactics but man is it intense, SWAT 4, but get some of the mods to upgrade the AI so you can control multiple squads at once.