40. Descent (Parallax Software, 1995)
A relatively unique take on first person shooting action, Descent was basically Doom put into the third dimension - you controlled a spaceship that could move and strafe in any direction and were set in a maze full of various robots and traps, tasked with rescuing a number of hostages, blowing the reactor and escaping before the whole place goes up. It was a bit hard to adapt to (especially if you didn't have a flight stick handy and had to make do with a mouse-keyboard setup), but it was visually impressive for the time and it played great once you adapted to it. The later levels do tend to get aggressively hard, especially when enemies with powerful hitscan machine guns start to become common, but nonetheless, Descent is a great time.
39. Commander Keen in Goodbye Galaxy! (id Software, 1991)
38. Toonstruck (Burst Studios, 1996)
37. Carmageddon (Stainless Games, 1997)
36. Lemmings (DMA Design, 1991)
33. Tetris (Alexei Pajitnov, 1984+)
32. X-COM: UFO Defense (Mythos Games/Microprose Software, 1995)