Dragon Age INQ is a good choice... was one of my favorite areas, too, and a good argument for why day/night/weather cycles may not always be better (i.e. if you're only going to spend a couple hours in an area... I'd much rather have a single 'perfect' atmosphere than a random chance at contrasting atmospheres). Obviously, Witcher 3, too.
I want to say Swamp of Sorrows in WoW.... But I'm biased because my Orc Rogue kinda lived there for 2-3 weeks during Beta 2 when the Level cap was.... Lv39, or 45 I think it was. Probably the Lv45 phase (cuz Lv39 was probably Scarlet Monastery and then I guess 45 must have been the Hakkar Temple phase). Spent a really long time always leveling and using it as a staging grounds to explore the nearby Alliance lands.
I hated Dustwallow Marsh though, even though I love ports and ogres. The sky was too clear and visible through the burnt tree. Something about too much open sky ruined the atmosphere, the way a good swamp kinda smothers and envelopes you (see SoS).
Even the dwarven Wetlands were better, and I wasn't fond of there either after the first two awesome Dwarf zones.
MGS V has a small but pretty cool swamp, too... Looks great when it's raining, I like to do sort of G.I.Joe 'Musk Rat' approaches there:
-
https://youtu.be/yH6SauFZfmE?t=918
-
https://youtu.be/LtlEfiTXt1I?t=1613
MGS 3 though probably had one of the best 'presented' sort of swamp experiences though (I think that one still swamp, on account of the flora). I mean, alligator head, the flying overhead search lights, shooting and eat fish and fruit, and then swimming into the next area to snipe The End early