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
Maybe it's nostalgia, but I agree that it was a sweet spot for game development. Developers and artists were more confident with making games in 3d, and they could do it cheaply enough that even big companies would publish pretty experimental games.
Then the shift to HD happened a budgets and dev times skyrocketed, leading to the dreaded Brown and Bloom "Realistic" Third-Person Shooter with a bald protagonist.