not really
but my first experience with 3D and 3D motion was mario 64

descent on the pc probably woudl have caused some motion sickness

Homeworld... the sense of combat and exploration in 3d (not just flat landscapes) was both a challenge and a motivation, but also the lore and the design has a sense of uniqueness that I haven't felt again with any other game.

Most recently F.E.A.R. - it's an intense atmospheric corridor shooter that was really compelling after I got back into PC gaming.

Not in for giveaway, "Garret, I'm slipping..." but +1 to OP.

I was completely blown away by BioShock 1!

Hexen or Heretic, can't remember which I saw way back then. One of the Wing Commander games (had movie cutscenes).
Baldur's Gate 1 & 2.
The original Half-Life.
Rainbow Six.
The Jane's Fighter jet games.

I forgot about the Thief games. They were amazing, the immersion from the audio alone got me hooked.

The first Deus Ex. For all of it's many many flaws it did things I have not seen utilized better since.
GTA: San Andreas. Absolutely jaw dropping the first time I saw it on PS2. The best "look at all this shit you can do!" game. (I don't consider bowling and Yoga to be great side activities in games. :P)
Skyrim gets a lot of flak for certain weak game mechanics but I don't think I have ever seen a game close to the scale of it.
And I will 2nd the guy who said Empire Earth as well! :D

Garrett, I'm Slipping!

C64: Mercenary, Paradroid, Impossible Mission, Spindizzy, Exile
Amiga: Wing Commander, Civilization, Microprose GP, Hunter
PC: GTA then Driver then GTAIII in a head popping chain, Outcast, C&C, Fable, Burnout Paradise

Actually, before there was GTA there was APB:
http://www.mobygames.com/game/c64/apb
I must have been 9 or 10 when I pre-ordered the C64 version from a trade show after being blown away by the Atari arcade machine

Just Cause or GTA
Many games are stressing and one might wonder why players enjoy them. Just Cause is amongst the very few games that I find extremely relaxing. It features a huge environment which you are totally free to explore if you are not interested in the missions. I spent hours exploring, diving, skydiving, driving all kinds of machines... And I took much pleasure in it. Back from work, you can swim, sail a boat in the sunset and after a few minutes you feel relaxed... Everything is arcade-like and easy. You can land a Boeing on a beach with the 4 arrow keys. It is almost impossible to die. I consider this game a holiday simulator. Truly a delightful experience.

Another game that I find very zen is Supreme snowboarding: riding with the sound of the wind and the snow under your board.

The nomad soul
Because however stupid and cliché it may sound, while I was playing it, I felt like having a second life. This game is so immersive, you cannot help being caught in it.

Dreamfall which is available here on GOG
Because it is the most moving experience I had in a videogame. I expected a mere good adventure, I was not prepared for this. Some moments in the game are really heart-rending and left me dazed.

F.E.A.R. 1
I have played hundreds of shooters. The context (enemies, weapons, environment...) changes but it is more or less always the same thing. This game offered something different and new in terms of gameplay.

I moved to Ottawa, Canada in January 1999 for studies. While in the Rideau Centre that freezing winter I saw a strange shaped box in an Electronics Boutique. It was Thief: The Dark Project. I bought the game and the next week or so of my life was intoxicatingly wonderful. I was Garrett. Never before and never since had I been so immersed in a game.
Being a stranger in a strange land and terribly homesick at the time the game also lifted my spirits.

Now I'm here at GOG, a Steam refugee and newly formed anti-DRM Hammerite. I'm waiting patiently for Divinity: Original Sin. In the meantime I would love to replay the Thief games.

I'm a taffer.

well blowing my mind would probably too much said but the games that really surprised and impressed me are Antichamber and Kairo

btw: "Garrett, I'm slipping!"

Immortal Defense is the scariest game I've ever played. Holy shit why are the option controls talking to me? Why am I talking to the turrets? Why am I playing this game at night in a dark room? and, of course, I had no idea games could do that.

Somehow, miraculously, considering the themes it deals with and the overwhelming weight of awful and offensive mass media baggage attached to them in the popular consciousness, Primordia gets its ethics exactly right.

Recently, reminded me how it feels to be a fan of something unironically and to be actually<i> immersed</i> in the game. By "immersed", I don't mean "wow, I almost forgot it isn't my own life" (because the game is deadly and continuity is patchwork), and I don't even mean "duuuuude, I really like it, like really a lot" (although of course I do). I mean emotional investment and deferring to the writers' authority on deciding the course of the story. As in "this character better survive because if he doesn't, I'd be saaaaaaaaaaad" vs the usual "this character better survive because if he doesn't, the game is shit and the writer is an idiot". Other games that achieved this significant feat include [url=http://www.gog.com/game/defenders_quest]Defender's Quest and Anodyne.

Morrowind was pretty impressive graphically when it was released. It no longer is.

Must have been the first time I heard a game using a proper soundcard, from PC speaker to Soundblaster! Absolutely incredible!

Can't remember the game though :P

Other than that, Wing Commander 4 and Warcraft 2 blew me away. WC2 especially, coming from the first warcraft - it was beyond amazing

I was pretty blown away when games started using pixel shaders for water effects.
My graphics card couldn't handle it, but I remember playing Star Wars: Battlefront at a LAN party and seeing a mate's screen and thinking "oh my god, it's beautiful!"
Pirates of the Caribbean also really impressed me with the water effects, and lots of little details, like the tiny lizards running around in the Jungle areas.

Other than that, Psychonauts blew me away completely, both with level design and story/characters.

Same with Anachronox, each new world was just amazing to explore.
I could see how one might think it was a bit mishmash or silly with so totally different worlds, but each one was so brilliantly executed.

Baldur's Gate! It was my second RPG (after Fallout), and it was something amazing back then. I couldn't stop playing it.

Probably Deus Ex: Human Revolution.

Loved the symbolism, the story and the overall world design.
Less cyber punk than the original, but still a good game.