Hmmm...It's kind of hard since I've never been a true fan of any game, meaning that I would've gathered some side merchandise on it.
I can name some games that I consider in considerably high regard:
Blade Runner
MDK (the snowboarding bit was on of the best things ever anywhere)
Supreme Snowboarding (aka Boarderzone)
Duke3D (the first game and the last game that I was so enthusiastic abot that I modded it)
I'm hesitating whether I should add Planescape:Torment here since it was also AWESOME
but its a different kind of thing...

<hedonismbot>No need to explain, I too have known... unconventional love</hedonismbot>
PST is a genuine masterpiece of gaming, it would have gotten even more rabid fans if it hadn't asked people to do the unthinkable... READ!

Zork: Grand Inquisitor. It is the perfect adventure game, in every way imaginable. If God made an adventure game, this would be it.

I'm atheist. Who is this "god" you speak of?

Only one of the most violent fictional characters ever invented! They should make a game about him, it'd make manhunt look like a friendly cuddle simulator

With no hesitation, for me it's Flashback (aka Flashback: The Quest for Identity). I've played it so many times on my Amiga (and on UAE now). That game has such a great universe, full of movie references, incredible graphics for its time, a good story, great gameplay.
I'm also a big fan of Another World (aka Out of this World), also on Amiga. An incredible game for its time, and made by only one person (Eric Chahi), if we except sounds and music. Published by the same company as for Flashback (Delphine Software). Here also, an incredible universe and a good story.
Dark Forces has also a big place in my gamer-heart. As a Star Wars fan, this game was the first one that make me feel completely *IN* the SW universe. Great story (for a FPS), great depiction of the SW universe, incredible level design, and one of the first *intelligent* FPS (you don't have to just find the red key, open the red door, find the blue key...).

You're retarded, you know that right? I'm not talking about Russian Tetris man. I'm talking about Intelligent systems Puzzle League, you idiot.

I had never seen this 3DO version, it seems really really nice.
The PC remake was the 15th Anniversary Edition, re-made by the original creator, with advanced backgrounds but still in the same original style. A must-have ^^
For info, there was also a sequel to Another World, called Heart of the Alien, made only for the Sega Saturn, but not by the original creator...
The problem with Fade to Black (even if I liked it very much at its time) is that was one of the first all-3D 3rd person game of that style, and has became old very very fast. Still interesting when you're curious about post-Flashback events.

u're right! somehow i forgot about another world sequel [maybe becouse it wasn't avaible at amiga or pc].
but - a little dementi -> [url=www.mobygames.com/game/sega-cd/heart-of-the-alien-out-of-this-world-parts-i-and-ii]Heart of the Alien[/url] was avaible only on Sega CD ;) - the generetion before Saturn.

I just wanted an excuse to post the video. Sheash.

Brentalfloss was good until he became famous. His latest one (SMB2) really, really sucks. DuckTales is his last great one.

I don't even like the DuckTales one...

Master of Magic hands down. Although I really like Ultima 7 and the original Ultima Online (in it's first year or so when it was challenging).
I liked Master of Magic so much I attempted to recreate my own version and came very close to finishing which is pretty good considering my skills.
http://www.machinations.org/mom
(Note: it's not open source anymore)
Anyway, MoM is a great underrated game!