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
Absolutely love the mid-late 2000s era of normal maps, stencil shadows, and real dynamic lighting. Absolutely Doom 3 & Splinter Cell, I'd also throw in FEAR (a style which they threw out in the much worse looking sequels), and Riddick: Butcher Bay. Give me more games where you can shoot lights out and turn an area just absolutely pitch black.