It could be anything from Movies, to Anime, to Video Games, and even TV Shows.
For me its the Risk of Rain OST. Its really powerful and it serves its purpose well and it might as well made the game for me.

https://www.allmusic.com/album/what-a-blast-architecture-in-motion-mw0000824578
haven't seen the movie, but i love the soundtrack

and the https://en.wikipedia.org/wiki/Tron:_Legacy soundtrack

and https://en.wikipedia.org/wiki/The_Saint_(soundtrack)

edit:
https://en.wikipedia.org/wiki/Wing_Commander:_Prophecy ost is also very nice
more like a movie soundtrack than a video game one

Nier: Automata takes the cake for my favourite vidya OST.

Bladerunner 2049 for movies

Anime is tough, as the OSTs usually don't play a big role in the show, but I'd have to say Kill La Kill

Blue Dragon & Dark Cloud (1 & 2) both have my favorite OSTs, and it's really tough to pick between any individual one since I have different reasons for why I like the OST. This being said, I also like Undertale OSTs, each one tells a subtle story.

I haven't seen enough movies to say that I like any particular, but one specific scene from King Fu Hustle comes to mind whenever I have to name a kickass beat. (Link)

And, finally, anything from Overlord captivates me as well. I really liked that anime and I'm glad I was introduced to it, too bad I need a prime account to get the latest episodes 1 week in advance.

Mass Effect 1 had a soundtrack that referenced great soundtracks from other IPs, while still managing to create something unique and memorable.

https://youtu.be/EuXOr1CcZsk
https://youtu.be/IitCQCaKi3E

metal arms glitch in the system ost is pretty good (except the first one) . particularly the rat race one

also when i'm in a mode to escape into enchantment land I listen to phoenotopia ost

Movie - LOTR Into the West

Game - Ozar Midrashim (feel free to guess where from)

Anime - Don't watch much anime, but N G Evangelion, Kill la Kill and Ghost in the Shell have nice ones.

I love older edm from the late 80s to 90s. It's kinda obscure but I think the saturn/pc version of Wipeout 2097 has a great trance ost. Here's a playlist (the album art says playstation but it's the saturn version)

Also I've got some game rips of castlevania and castlevania dracula's curse from using a modded nes and outputting it to 24 bit flac. It's way better than any official soundtrack or game rips in nfs format, they just don't do it justice. This here is like playing it for real on a tv with a great sound system. Mind if I share it with you guys? It's not my rip but I added tags and album art to them, the guy I got it from put no track info or anything on them.

Half-Life 1 and 2's soundtracks are pretty awesome.

Alan Wake.
Ghost Trick, Legend of Grimrock 2 and Undertale OST were also good.

But most of game music is like elevator music to me: it's just something that's there, and I hardly even notice it.

It's difficult to choose. I think Stellaris OST takes the cake for now. I have played games for 21 years and have many favorites.

The Persona video game series has some great music if you're into Japanese stuff (most of it is sung in really bad English though).

You personally should know this since you see me listen to this all the time. The Skyrim and Dust: An Elysian Tail OSTs.

The first Trails of Cold Steel game has some pretty good music, and just to link a few:
Music that plays in a massive plains, and I mean takes quite a while even on horseback to go do the quests in the area
the music that appears when you have to do investigations of a mysterious school building near the academy a good deal of the game at
The normal battle music sounds pretty great to me, as well

emmybecca said:
In the End

...the Linkin Park song? I don't think that counts as OST.

But since this thread is open again: forgot about the Persona series.
In particular, Maya's Theme from P2 is pretty neat. And the P3FES is good too.

Genjar said:
...the Linkin Park song? I don't think that counts as OST.

But since this thread is open again: forgot about the Persona series.
In particular, Maya's Theme from P2 is pretty neat. And the P3FES is good too.

I like the instrumental of Key plus Words (P4)
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Finding one favourite is difficult, I hope mentioning more isn't a problem ^^

DoDonPachi DaiFukkatsu Black Label.