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
Probably between 1995 and 2004/5. I really liked the mix of realistic and cartoonish styles we had during that period. Also, I think game genres weren't completely established yet, so developers were much more creative and had more freedom to experiment with gameplay and graphics.