First person shooter?

I'm hoping this is the right place to ask about first person shooter games. I couldn't find another appropriate community. I'm getting the itch to play a good FPS on my iMac 27" Retina (Late 2015) running High Sierra. In so many words, I enjoy these games, but I suck at them. I've played many on my Xbox 360 with much frustration, because I'm just not proficient at using the gamepad. (Personally, I don't see how anybody is. Lol) Using a mouse seems to be the lesser of all evils. I still get my butt blasted away when I play online against other players, but at least I'm not experiencing the "yoyo effect" of the gamepad: move the cursor - oops, too far, move it back - oops, too far, move it back the other way now - oops, too far...ad infinitum.

I saw "Call of Duty 4 - Modern Warfare" in the Apple app store. In the minimum requirements, it specifies ATI Radeon X1600, or NVidia Geforce 7300: 128 MB VRam. My iMac video is AMD Radeon R9 M390 2 GB graphics. I have a sneaking suspicion that although I've got enough VRam (I think), I probably don't have the right kind of graphics hardware. Can anyone confirm?

Also, can anyone suggest a good FPS game where I might stay alive for more than 8 nanoseconds without getting blasted to kingdom come?