Don't really think I had one. JRPGs had a shit ton of FMVs with 3D graphics, in-game in anything never matched those, so I was eagerly awaiting when gameplay looked just as good as those cutscenes.
Sonic 1 was the first time. Cart goes in, console turns on and then the best looking game I'd ever seen appeared on the screen within seconds.
Big jump from the Commodore C64 loading tapes.
After that, I spent time in arcades so home consoles never impressed me again. Until arcades died.
When you get teleported to the dark world in A Link to the Past. The parallax when you're on top of the pyramid blew me away and I remember thinking that I was seeing the peak of video game graphics.
Especially the quality of the animations really impressed me. It even impressed my grandmother and because my grandfather was happy about my granny being impressed he even granted me 1 more hour in which I could play the game on his PC :D
A very particular wall in the Runway level of Goldeneye 007. It had what appeared to be depth - think super early bump mapping - and I was just blown away. I remember showing the wall to people and saying "IT LOOKS LIKE A REAL WALL!".
As somebody who skipped the entire N64/PS1/Saturn generation because I was legit disgusted by early 3D graphics and the abandonment of 2D: I've never said this.
There was an MLB game that launched around the beginning of the PS2's life, and I remember booting it up with my family and thinking WOW, this looks SO GOOD, where are we gonna go from here??? Simpler times, man.
Not sure I've ever had that exact thought. I do remember seeing Battle Arena Toshinden running at the store, around the time the original PlayStation launched, and being blown away.
I remember calling my mom into the room to show her how cool that looked and stately emphatically—something to the effect of—this was the pinnacle of gaming graphics.
I've honestly never said that games can't look better. I've always compared how graphics look to real life and high budget movies. It may be unrealistic to think that way, but I have.
TESIV Oblivion was the first time I thought "if all games looked this good and graphics never advanced past this I'd be fine". it was just super real looking back then which is now obviously super hilarious considering the potato faces and whatnot.
Those PS1 final fantasy CGI cutscenes. Figured we'd have graphics like that for gameplay at some point after many decades and that life-like realistic graphics was something that wouldn't be achieved until after I died far in the future.