I wasn’t expecting to see INFRA mentioned but it’s one of my favorite games for a lot of the reasons you mentioned! It really had a sense for exploration and environments to tell more of the story. And it really is part puzzle game without having any single gimmick like other first person games. It reminds me a lot of Half Life 2’s puzzles (which makes sense since INFRA was also built in Source as far as I can remember).

I’m really itching for more expansions or games like it. Not sure what happened to the DLC they were working on, but there were some groups working on mods.