The original Zork... text-based PC gaming at its finest. That same summer, I programmed my own PC game (on a Commodore) from a published script in Dragon Magazine. That's right... the "game" was raw, uncompiled code that you had to manually type in character by character by character (about 5 or 6 large 'zine pages worth) and God help you if you made a typo. Took an entire weekend to input, compile and debug for a simple thing that played out in like 5 minutes, but it WAS a game!
It's startling to see how far we've come.
If you mean what THIS crowd would consider as a "PC Game" I'd have to say the original Wing Commander... that game really showed what a 386 processor could accomplish. I played it on the Battletech Center's inventory control PC. I remember buying Wing Commander II and MARVELLING that it actually came on *15* 5" floppies... retty amazing, considering that my PC then (a state of the art 486-SX PC running at *20 megahurtz with 2MB (that's MEG, not GIG) of RAM*) only had a 100MB hard drive, so installing the game basically used up over a quarter of my hard drive space after decompression.
After we'd play, we'd go kill a brontosaurus with pointed, flame-harded sticks for dinner... :cookiemon