For me it was encapsulated by doom 3 for the most part. Games with strong dynamic shadows like splinter cell chaos theory and stalker with a mix of shiny specular effects is timeless for me. When I go back to these games the shadows still feel as good as they did when they came out and the lighting perfectly crafting the mood. A lot of modern games now even though their fidelity on paper is much better just always feel extremely flat to me and don't pop out of the screen like they used to. It seems like they're missing contrast and UE5 seems to make this even worse where all the games using it just look like mush
I don't think i have any, well maybe the moment where games were jumping from 320x240 to 640x480, that difference was huge.
Current one is fine too, except most of pixel art. Some of it do look good, but for fucks sake most of pixel art just look like soulless, lazy and cheap imitations of the abovementioned two eras and for someone who did played then it does look like insult smeared with shit.