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
Gran Turismo 4 and the Silent Hill games (except the PSP/Wii version) were also very good. I think there were a few other fighting games and RPGs with very good graphics. And speaking of PSP, Parasite Eve 3: The 3rd Birthday looked just like a PS3 game on PSP, which is impressive.