i will say, that the moment i felt was incredibly unique and moving was Mission 8 of all places. Coster's fanboying over Purple Magic for a few missions and the indie songs those guys made culminated in
My Blue Sky Home and what makes this song stand out in the OST for me, and in-game, and the mission so unique... is that as the Purple Magic guys are dying off in-game, the song
loses instruments. not even the most pretentious or esoteric indie-developed game has done this, it has to be a world first in video game music composition. it's so unhinged in a good way; it's super cool from a ludonarrative harmony perspective. it blends actual singer-songwriter content with video gamey BGM seamlessly.
characters in operas don't just have their own themes but those themes are interwoven in very odd ways sometimes. dynamic musical motif insertions, stuff like that. the whole early game is very operatic.