A 7750 isn't necessarily awful, but you'll have to put BF3 on low settings if you have any desire to play at a smooth framerate.
Definitely Get CoD 1, 2, and 4. Battlefield 2 and 2142 are also quite nice
Most FPS games nowadays are primarily known for their multiplayer gameplayer (cooperative play online). However, if you like to play single player, then most of them are awful... including the Call of Duty and Battlefield series.
There aren't many good single player ones... but a couple good single player FPS games include Far Cry 3 and Metro 2033... though both have elements that are unrealistic (like mutants in Metro 2033). You also might want to check out the older Half Life 2 if you missed that, as it is (supposedly) one of the best FPS games of all time (but it also involves elements which aren't realistic, like aliens).