Zork. That is about as old school as you can get. I remember playing it in third grade, getting my forearm cut off then going to some class later and finding out exactly what a forearm was. Needless to say I was quite impressed that my character could walk around missing part of his arm. My cousin Tucker always tried to make it do bad things like, "Attack Penis" or "Cut off Dick". The game never let him get very far. I remember it now, traveling in an arbitrary direction, picking up all I could carry. Finally coming upon and entering the house, taking everything that wasn't nailed down, and moving the carpet to find a trap door. After wandering in the darkness for a while eventually getting eaten because I could never remember to light my torch.
The first game I remember falling in love with on my PC was the original Archon. Fairly simple "chess-like" game, but damn did I spend hours on end playing it. That was on my $5,000 x286 Tandy! And the other extremely memorable game is of course the original Civilization, which I'm amazed ran on that thing! There were several other dinky games I played on that thing, but those are the 2 I remember the most.
Of course, there's Descent (Destination Saturn) as well. Never have gotten very far on that, but good fun stuff all the same. Love the music.
Seeing those games hurts my eyes. I went from having perfect 20/20 vision at the beginning of summer in grade 6 to -4.25 at the beginning of grade 7 because of sitting in front of an EGA monitor. I remember spending hours on Montezuma's Revenge, Jumpman, Grand Prix, and a whole bunch of others.
I used to play Outrun and Shinobi on my old IBM PS/2. At school I spent hours and hours playing Oregon Trail. Unfortunately my doodz were always dying.
Here is one of my favorite series wing commander one of the defining moments of gaming history. Think New BSG and you have a idea what wing commander is like artistically speaking here are some pics from various games. WC1 http://media.arstechnica.com/articles/paedia/gaming-evolution.media/wingcommander-1990.gif Here is a pic from the third one http://media.arstechnica.com/articles/paedia/gaming-evolution.media/wc3-1994-small.gif Notice how four years difference in technology can change a game. These games always forced people to get a new system. First it was soundcards then the 5th one people would buy voodoo cards for specific glide graphics effects. This is a classic series you should try.
Armor Alley, the Spectrum Holobyte version of Tetris, Super Munchers, Glypha, Glider... so many classic Mac games.