I played my first computer game on a Commodore C64. It's nice to remember those times. It used 5.25" diskettes to store and load games. Those days Accolade was the only game producer I knew, and its really nice games (Grand Prix Circuit, Test Drive, etc.) kept me in front of the monochrome monitor all day. I really can't remember where I put that monitor. It would have been nice to see a Pentium IV PC (and NFS Underground) running on a monochrome display.
I'm looking forward to hearing how your first gaming PCs were.
My first true PC game was Wolfenstein 3D. I lost many nights in front of my first AMD K5 PC trying to find a way out of that maze of walls and doors and kill the big bad nazi at the end. Here are some screenshots of the game, for those nostalgic gamers out there: