As a big Raymond E. Feist fan, that game was just the ultimate child geek experience for me. I still remember that awesome spell you could cast that would make sweet nectar sweat out your enemies pores and swarms of fairies would come and bite them to death. I had pages of trial-and-error letter lists for the lockboxes with riddles I couldn't figure out. LOVED that game.
I was really interested in Darklands, but as a child I didn't 'get it' and so ended up in difficult situations and dying all the time, so I lost interest.
Starflight was huge, don't remember the game much, but remember the annoying decoder wheel you had to use to play it, hehe.
I was also a big fan of Sentinel Worlds, I can still hum some of the music.
For RTSs, I cut my teeth on Dune 2 and C&C. I bought my first sound card for Dune 2, and I remember the amazement when I heard that 'high quality' sound coming out of my PC. C&C was even my first real 'online' game (aside from BBSs), as you could use your modem to dial up and connect to another C&C user and fight head-to-head.
I also fondly remember every single Sierra game, that company put out some awesomely fun stuff until it went all point-and-click. I learned to type on those games (and their non-Sierra text-only precursors). I still type faster than anyone I know (though it helps being a Linux admin keeps those skills sharp). I remember trying to play Leisure Suit Larry and always had to ask my parents to help me answer the questions you had to answer to prove you were an adult and could play the game. I thought they were serious content protections, so I always thought I was doing something so naughty. Of course it was just a joke, but I didn't know that. The Space Quest series was hilarious.
Pretty much all of the classic TSR 'gold box' D&D games were great experiences. For some reason I recall not really getting into 'The Curse of the Azure Bonds' though, can't recall why.
Something about Omikron: The Nomad Soul really drew me in, too, though it's not nearly as old as many of these games, it's just one I don't ever hear anyone else talk about. I don't know what it is, but I got REALLY into that game.