Asura's Wrath's musics are interesting, but listening to them can be awkward since they may sound like religious music.
Catherine's spin on classical musics on its OST was a surprise, but a good one nonetheless.
Celeste's OST is great for setting up them mood of their respective parts in the game, with some musics even being relevant for the message being given.
Dissidia 012, being a crossover of multiple Final Fantasy games, has many iconic musics, and the original musics are also pretty good.
Final Fantasy VI and VII's OST work pretty well for their respective motifs.
Final Fantasy XII is great for orchestral musics in both versions of its OST (PS2 one, and remaster one), as well as not following the cliché of music styles you'd expect for a given region.
The God of War franchise has plenty of interesting musics in that vocal Greek style (gonna confirm at some point if it's indeed a Greek style, though).
The Mary Skelter franchise is also great within its premise, with musics being played in a rhythm just odd enough to sound wrong, but without being easy to pinpoint what is wrong.
Odin Sphere and Okami have good musics for their contexts, although, alone, they sound kinda meh most of the time.
Persona 3 (all 3? 4? 5? versions) follow the same idea as Celeste's, if not being even more incisive with how long the game is.
I find Shantae and the Pirate's Curse to be a gem in so many aspects, and the OST is no different.
Songs for a Hero is, well, a game whose whole premise is that the protagonist sings based on what is happening in the gameplay.
Game with good environment music #6549813: Starbound
And Hearts of Iron IV has musics from Sabaton, nuff said.