Ar Tonelico 2 has one of the most beautiful musics I've heard, not limited by music. Not too surprising, given how the entire franchise is basically about glorifying music to divine levels and brings top notch singers like Shikata Akiko and Shimotsuki Haruka to sing songs like METHOD_IMPLANTA and EXEC_SOL=FAGE/.. The BGM is also great, with tracks like Rustling Throb Cloche.

Other great OSTs that never leaves my phone:
-Einhander (Sample: Bloody Battle)
-Omega Boost (Sample: Orbital Flight)
-HellSinker. (Sample: Apostle of the Seed)

Finally, special mention to Space Invaders Extreme 2. I wouldn't say it's the best OST but it's the most fun example of adaptive music I've seem (heard?).

Citizen Sleeper, Mass Effect, Disco Elysium, Final Fantasy 7 Remake, Neon White, Valheim, Minecraft, Sable.

Star Ocean 3, Yakuza: Like a Dragon

Primarily a mix of Old School RPGs (FFVI, Secret of Mana, Chrono Trigger) and some current RPGs (Persona 5, NieR: Automata)

Mother soundtrack had been in the rotation for some time! "Fallin' Love, and" forever favorite.

Divinity Original Sin 2 is my go-to.

I see several people naturally mentioning the Minecraft OST, there are two resource packs I highly recommend if you want a more nostalgic experience.

• "Balanced Music" is a great pack on Modrinth that removed the biome specific criteria and re-balances everything so you do not keep hearing the same caves & cliffs song every 10 minutes.
• "C4Music" is another pack on Modrinth that removes the newer tracks (post Nether update if memory serves me right) and only has original music + some of the unreleased tracks.

To answer the question myself though, other than Minecraft of course I would have to say Terraria, OpenTTD, Ocarina of Time, RimWorld and Celeste among many other titles.

torn between Rain World and Hyper Light Drifter

Riven gives me goosebumps every time.

I haven't even played Machinarium or Samorost 3, but both of those soundtracks are masterpieces.

Big fan of ffxiv's ost. Sokens work is fantastic. Destiny 2's music as well has been fantastic, despite the game getting a little stale.

Every Korean anime online game i've ever played has had an unnecessarily good soundtrack. Maplestory, Mabinogi, LaTale, S4League, GunZ: The duel, the list literally never ends.

Warhammer 40,000: Mechanicus

I looked over the whole list and noticed it's lacking one Rise of the Triad 2012 and Distance.

I would mention Rez and DJ Max, but it feels a little silly to mention Music based games for good OSTs.

And apparently I need to go listen to the OSTs for rain world and journey. They got multiple recommendations on here.

Cowboy Bebop, all albums

All 3 Xenoblade Chronicles games have some of my all-time favorite game music

For me it's Skyrim. Streets of Whiterun, Masser, Jerral Mountains, Under an Ancient Sun, so many tracks that just instantly transport me back to the world I was immersed in throughout most of high school. They bring a sense of peace that comes from exploring in a simpler time.

Final Fantasy XIV. I'm so excited to hear what Masayoshi Soken will cook up next. Other ones to mention are Guilty Gear Strive, MegaMan X and Zero series, and The World Ends With You.

Shocked and appalled at the lack of Resident Evil/BIOHAZARD representation.

The survival horror classics of the 90s are simply unmatched. One of my absolute favorites is the OG RE2's Marshalling Yard, both halves.

I really enjoyed the OST of the Ace Attorney games (especially the first one), Shadow of The Colossus, Kingdom Hearts, Hotel Dusk and Xenoblade Chronicles... I could go on though.

SimCity 4 openTTD's openmsx (admittedly I have a soft spot for MIDI in general) DOOM (1993 - again, it's MIDI) Need for speed underground 1 Tony hawk's Pro skater (N64) Factorio Minecraft (the C418 era particularly) Terraria (this is just awesome and makes the game so engaging

The list goes on, but these are the ones I can list rn

I don't think I've ever heard a megaman track I don't like

I'm a fan of the OST from Mount and Blade: Warband. (this video is in alphabetical order. The main theme starts about halfway through.)

Final Fantasy VII (all of them), Kingdom Hearts (all of them), Celeste and Toy Story 2 on the PS1 immediately come to mind.

Edit: Oh my god, how could I forget all of the personas, especially 3.

These:

https://www.youtube.com/watch?v=3D0YwnEWK-Y

https://www.youtube.com/watch?v=6tXuSsEnXJo

https://www.youtube.com/watch?v=BvQHvaKuN_E

i loved "the flame and the flood" for what it was, though i wouldnt add it to my playlist and all

some of inon zurs work on fo4, especially the settlement/town idle captured this frontier/post Apocalypse vibe i absolutely loved

Guild Wars 2 for sure. It's one of the games where I never turn the music off.

Granado Espada is a favorite classic and then there's Suikoden 2for the nostalgia

Deus Ex 1, Vampire: The Masquerade: Bloodlines, and if it counts GTA III.

Steven Wilson’s soundtrack to The Last Day of June is absolutely spectacular.