When all the rumors of a Silent Hill remake were swirling last summer, I dove into listening to the first 4 games' soundtracks. They really have such an ethereal quality that is hard to match. I particularly love Silent Hill 2's atmosphere just based on the music alone. There were a few days were our city was blanketed with smoke from wildfires, and boy did those tracks feel a bit more real as I walked through the deserted parks.
Another series with great music is Ace Combat. The soundtrack for 7 was on a weekly rotation for awhile after I finished he campaign. I've only really listened to the OST for AC4 and AC: Zero, but I've heard there is a lot of love for the other games as well.