Oh geez, I don’t think I could even pick one per genre, much less one in general. Here are a whole bunch of my favorites.

Notes:

  • There are some excellent games that I have left off of this list because I don’t personally care for them as much (e.g. Super Mario Bros., Star Fox 64, and Half-Life 1), or because I’m familiar with them but don’t have enough experience to make an informed opinion (e.g. Fallout, Earthbound, and Myst).
  • I am primarily a classic/PC gamer. The newest console I own is XBox (not 360), and my PCs are a couple years old, so I haven’t played many really recent games. I still think the SNES is the greatest console ever, followed by XBox 360 and PS2. (My least favorite are GameCube and Wii. Also, I really wish Sega could make a comeback; the Dreamcast is really underappreciated.)
  • *** = If I HAD to pick just one for each genre, I’d PROBABLY pick this one.

Platformer:

  • *** Super Metroid (SNES)
  • Donkey Kong Country 1-3 (SNES)
  • Super Mario World 1-2 (SNES)
  • Mega Man X 1-3 (SNES)
  • Sonic the Hedgehog 1-3, Sonic & Knuckles, Sonic 2-3 & Knuckles (Sega Genesis)
  • Super Mario 64 (N64)
  • Little Big Planet (PS3)
  • Portal (PC, Mac, PS3, 360)

RPG (Role-Playing Game):

  • *** Chrono Cross (PS1)
  • Chrono Trigger (SNES)
  • Baldur’s Gate 1-2 (PC, Mac)
  • Diablo 1-2 (PC, Mac)
  • Super Mario RPG (SNES)

RTS (Real-Time Strategy):

  • ***StarCraft (PC, Mac)

TBS (Turn-Based Strategy):

  • *** Heroes of Might and Magic III (PC, Mac, Linux, GBC)
  • Civilization IV (PC, Mac)
  • Age of Wonders (PC)

FPS (First-Person Shooter):

  • *** Half-Life 2 (PC, Mac, PS2/3?, 360)

“Simulation”:

  • SimCity series (PC, Mac, with progressively older games available on more systems)
  • RollerCoaster Tycoon series (PC, Mac [3], XBox [1])