Whooooops! ZORK/Adventure rates up there with my top ones as well. :-)
Adventure was the very first computer game I ever played. That was on an IBM-360 Mainframe. :-)
Oh yeah who can forget Zork I-III. I even like the first non-text based Zork game because your character looked like Rush Limbaugh
The other great games for the early PC's were the King's Quest games and Archon (I'm surprised they never tried to bring this one back).