The only old-school computer I have any experience with is an Apple IIe, because that's what my school had when I was a young lad. Mystery House was the GOAT.
I had some friends that had Commodore Vic 20, 64, 128, Amiga but my first computer was a Laser 128 (Apple II clone). A lot of cool games for it. My favorite was Gemstone Warrior, kind of a randomized timed dungeon game combined with "dual stick" (via the keyboard) shooting mechanics.
Never really got into the C64, due to the load times on the original hardware... what's worth playing? The Ultima ports were pretty good, right?
Bard's Tale
Aliens
Epyx "Games" series (esp. California Games)
Impossible Mission
Inflitrator
International Karate
The Last Ninja
Defender of the Crown
Maniac Mansion
Lode Runner
Turrican
Bruce Lee
The Way of the Exploding Fist
Wasteland
AutoDuel
Skate or Die
Airborne Ranger
Pirates
Prince of Persia
Fight Night
Raid on Bungeling Bay
Barbarian