I've always been impressed with Resident Evil 6's China levels

Everything's just so densely packed with detail, both large and small scale. These exterior city scenes are massively helped by them being set at night and being lit mainly by neon lights, but there's just so many lights and signs everywhere it really makes things pop. All the interiors are jam-packed with all kinds of little props and wall decorations, and I really like the cramped, dirty and run-down apartment complexes you visit in the game despite them not being all that much fun to play in. They just feel really immersively lived-in.

Here's a really cool location from Chris' campaign that you only visit for a brief boss fight and have no reason to linger in. I didn't even remember this place from my previous playthroughs and probably assumed it was a generic video game dungeon level, but it's really interesting:

https://streamable.com/4ghdg2

You have this dark, grimy and trash-filled inner courtyard in an apartment complex. It looks like it's underground, but it's actually an open-air space that's covered by a netting with sunlight being blocked by the massive amounts of garbage accumulated on said netting, and you also have a dense tangle of electric cables and wires crisscrossing from building to building. Most of the courtyard is taken up by an older brick building that looks like it predates the apartment complex.

It must've taken tons of artists tons of work to design this intricate space that the average player is going to spend less than ten minutes in, and who aren't going to notice the nice environment art anyway since they're too busy trying to electrocute a giant boa constrictor while they're there