Over time: probably Contra on the NES, Tetris and Bionic Commando on the GameBoy, Operation Wolf and Sinistar in the arcade. DOOM, Duke3d, and XEvil on the PC. CS 1.6 and CS:S in college. The Gears series on the 360.

Then I had a decade or so gaming drought. More recently: Batsugun, Ketsui (Deathtiny and Death Label), Danmaku Unlimited 3, and Battlefield 2042.