uncharteds have always had a dark undertone. and is always a contrast with nate. also, the first teasers were also not the most jolly.
when you look at moments in uc1-3, a lot of it are not joyful. it is mostly focused around danger and mystery. finding skeletons and corpses, being trapped, etc. always apparent during exploration and solo adventures. there was always a clear separation between action moments i.e. gunfights and set-pieces. but apart from those, a lot of it are more "dark" (for a lack of better word).
i have always looked at it as looking at a beautiful piece but then looking at that one strange spot and sensing that something is off. it's that feeling that encapsulates a lot of moments in uc1-3. a lot of those come across during puzzles, traversal exploration, reveals.