Nethack is the ultimate game ever written for the PC.
It's the only game which made me skip school and stay up night after night.
I can still remember my first few games which all ended on level 1: "A mysterious force prevents you from going down."
Which ended up to be a DOS error: disk full! It was one of the first releases of Hack, one from the UVA. I think it was version 1.0.3
I still had a XT machine based on a 8088 processor and running DOS 2.11 whith just 2 floppy drives and no harddrive.