Damn my earlier memories are really foggy as a late 80's kid. I never owned any of the fifth or sixth console generations, and I think I sort of consciously avoided looking at those games. But for PC I think the earliest game that I remember having my young jaw truly drop for was Trespasser. Bump-mapping, interactive water, physics engine, large vistas. I absolutely loved the game as a kid (despite its myriad flaws). A year later Outcast dropped, with its fancy water shader and impressive voxel-based terrain rendering. Though I never properly played it at the time, I drooled over the PC Gamer articles.
After that I think I was mostly impressed with texture and art-direction, not so much technical details. Max Payne, Return to Castle Wolfenstein, the PC port of Silent Hill 2, they're all games that looked absolutely amazing when they came out. But to my eye they looked jaw-droppingly good. The original Mafia game was also a gem for it's big world and detailed characters and cars. It felt stunningly realistic.
There is a bit of a gap in my memory for a few years after that. I know I was impressed by Halo (and very disappointed that my GeForce FX 5800 could barely play it), but the next truly mind-blowing game I remember graphically was Doom 3. I absolutely loved the look, and the facial animations, of Half-Life 2, but Doom 3's heavy use of bump-mapping and stencil shadows just screamed next-generation to my naive mind. As luck had it I loved both games. Again miffed by my Geforce FX which had to run HL2 in DirectX 8.1 mode...
After that I think I sort of reached a point in my life where graphics drifted from its place as center of attention for me. It sort of coincided with the seventh console generation. I followed the Xbox 360 and Playstation 3 hype machine eagerly. And I think the general level of graphics development on display had risen so far by that point that I felt generally impressed, but began having a hard time picking out specific games graphically. Final Fantasy XIII I remember for its graphics. Since then I've gotten mostly hooked by gameplay, atmosphere, and art direction. Though I will admit that Cyberpunk 2077 is one of those games that I still think look absolutely bloody amazing every time I start it up.
I guess I'm growing older and harder to impress hehe
Thanks for inviting me to a trip down memory lane. That was fun!