PC Gaming

It might have been the first far cry game or possibly doom 3, I forget what came first.

Wolfenstein 3D

The graphics and gameplay were mind blowing at the time.

Apple II GS - The City & The Dungeon

Doom truly blew my mind when it got released. Graphics were so good that it felt like black magic.

Quake for graphics, Heroes of Might and Magic 2 for gameplay.

The first 3d(not top down) GTA game...the freedom to explore was epic

Siege of Avalon. I had played a few RPGs but SoA blew my socks off with the graphics and everything at the time.

Final Fantasy 8 for me. It was the first FF series I played and even after trying many others, still my favourite.

Squall was a moody douche but I still loved him.

Command & Conquer

Habbo hotel followed by Runescape. Habbo hotel was my first intro into PC games then Runescape consumed my life.

The first one that really got me and I just couldn't stop playing was Fables: The lost Chapters (the PC-Port of Fables 1)

Dungeon Keeper I would say. Possessing a fly for the first time what quite a surprise.

Trite, but probably the original Wolfenstein, quickly followed by DOOM.

Oregon trail... xD

I don't remember exactly if it was a DOS game but I really liked Dangerous Dave 2

Jane’s ATF. I’m sure it hasn’t aged well.

Hmm, not sure... possibly something from my childhood. Star Control II (now available free/open source as The Ur-Quan Masters is one of my absolute favorites, but I first played it at 6-7 years old -- and English is not my native language, so I can't imagine I understood anything at all about the story at the time.

That or Half-Life is what I usually point to as my all-time favorite games. Half-Life was pretty mindblowing; me and my friends spent a ton with it, so I think it's the best answer for this thread.
Not to mention that we played Counter-Strike so much that even 23 years later, it's likely to be the game I've played the most, despite barely playing at all after my teens.

MechWarrior 2. I recently AI upscaled the intro

https://youtu.be/cr_g_PDRmso

Little Big Adventure. That's the first one which looked so far and beyond what a console could do, in my mind.

When I finally upgraded from my ultra-budget NVIDIA GT710 to a GTX 1060, the Tomb Raider reboot blew me away from how good it looked

I distinctly remember "Redneck Rampage" being the first game I'd ever played with an install over 100MB and it blew me away - that felt absolutely MASSIVE at the time.

The physics engine in "Jurassic Park: Trespasser" also knocked my socks off. I wish that one would get a re-release on GOG or something; it's terrible, but I've got a lot of fond memories bumbling my away around that island.

Wolfenstein 3D. It was an incredible leap from what I'd played before.

Return to Krondor will always have a soft spot in my heart.

F/A18 Interceptor on my good old Amiga 500 :)

Diablo 2 absolutely blew my adolescent mind. It was also my first PC game!

I’d have to say the original Half Life. First time I ever felt like I was actually part of the story.

Minicar racing. My brother and I used to play split screen multiplayer on the pc for hours. Having mostly only played 2d games before, the 3d aspect of it really blew my mind

Half-Life playing deathmatch for the first time on a 56k modem, lagging like hell but when i saw someone else for the first running around my mind was blown haha