What is the greatest song from a game's soundtrack in your opinion?

Oh, no, what have you done to me? I got the unstoppable urge to write a huge list.... Sorry. :(

Anyway, these songs are great, but my choices are heavily influenced by context, how they fit the game and whatever mood they try to establish. Maybe some of these aren't so remarkable if you just listen to them by themselves. And I am kind of old. :)

I am going to separate these more or less for their mood. Don't listen to them in this order, necessarily. :D

FOR THE FEELS:

• Illusion, from Hellblade: Senua's Sacrifice... and the video raises its power even further.
• Still Alive, from Mirror's Edge. I do not understand why it fits the game so perfectly, or why it really gets to me.
• City of Tears, from Hollow Knight, better with rain. Hollow Knight has many nearly-perfect tracks!
• Setting Sail, Coming Home, from Bastion is two great songs for the price of one.
• The Spine, from Transistor. She's got an incredible voice.
• Adagio for Strings, in Homeworld, especially in context.
• Maenam, from Braid -- very meditative.

CHILLING/EXCITING:

• Ariel's Lament, from Soul Reaver 2 gives me the chills whenever I hear "Kain refused to sacrifice".
• Main Theme, from Chrono Trigger is such a classic.
• Turanic's Raiders, from Homeworld is both tense and exciting.
• Departure, from The Last Express because I am a sucker for violins.
• The Fight, from Prince of Persia The Sand of Time for blood pumping action.

THAT EPIC FANTASY MOOD:

• Guild Wars' Login Screen Theme sets the perfect epic adventure mood.
• Morrowind's Main Theme. This is the best arrangement of the Elder Scroll's theme song IMHO.

UPBEAT:

• The Stars, from SteamWorld Heist is incredibly harmonic, and very upbeat.

Cheers! :D

I love both Firewatch and The Flame in the Flood soundtracks.

Final Fantasy VIII
Also Devil May Cry games and both Nier games have very nice soundtracks.

Life is strange was mentioned before, but wanted to add my fav song used in before the storm
this one

The whole soundtrack is so good it's hard for me to pick one.

NieR: Automata - City Ruins (Rays of Light)

Alan Wake has a great soundtrack. Hope Alan Wake 2 sees the light of day!

The Poet and the Muse

Chrono Cross - Time's Scar

Grandia 2 - A Deus 🎶😪

...I can't pick just one... ^_^'
(Heck, I can't pick just one favourite within some games' soundtracks.)
I guess I'll just... list a bunch and just go with "those are all the greatest (For Now™)". :D

This one from FTL: Faster Than Light.. It's a really good sci-fi sounding theme.

The Darkest Dungeon's theme from... Darkest Dungeon. A bit different from most of the other soundtracks I tend to listen to. The game is already really good with its setting and atmosphere and this theme just fits perfectly for the final quests.

The True Final Boss' theme from Hitogata Happa. Yeah, ok, I have absolutely no expectations that anyone who might read this has actually played that game, let alone fought that that boss (that game is pretty hard), but I do really like the soundtracks of all the games in the trilogy its part of.

This one from Jamestown. Another very good Bullet Hell game with a great soundtrack.

This version of Noire's theme from the Hyperdimension Neptunia series. Those games also have a ton of great battle themes- like this epic boss theme from Megadimension Neptunia V-II. (That game has a different theme for Noire so technically I'm not breaking the arbitrary "one soundtrack per game" rule which I'm going with for some reason.)

Every. Single. Theme. From Sora's Soundtrack! ...Ok, ok.. let's go with... this one (but, really, they're all good).

This theme from Serious Sam 3.

Every theme from Giana Sisters: Twisted Dreams! Wow, I'm really bad at picking just one, huh? Let's go with, uh... this one.

This from Devil May Cry 1.
This from Devil May Cry 3.
This from Devil May Cry 4.
(There might have been a bit of a pattern there...)

Obligatory Half-Life 2 entry.

Every battle theme in Painkiller... er, I mean, this one.

This (and every other) theme from Rabi-Ribi.

Most of Hotline Miami 2's soundtrack but let's go with this one for now. (If you liked the first game's soundtrack, chances are you'd like this one too. ;D )

Pretty much every theme from Yakuza 0. Erm, I mean, this one.
Also this one from Yakuza Kiwami 2 (which also has a ton of awesome themes).

This theme from CrossCode. (And all the other battle themes.)

This theme from Double Cross. (And all the other battle themes... Wait, didn't I just do this? Ugh, who's bright idea was it to put two games with similar sounding names right after each other in my playlist... oh, right... I did that.)

This theme from The Legend of Heroes: Trails in the Sky.

This theme (and a bunch of other ones) from Indivisible.

This theme from The Messenger. (Ok, let's just say that every time I link the playlist I'm non-subtly implying the whole soundtrack is great so I'd stop repeating myself. XD )

This theme from Dead Cells.

This from A Hat in Time.

This from Particle Fleet: Emergence. (A game I'd imagine most people haven't even heard of... <.< )

This from RIVE. (Another mostly obscure game. :'( )

This from Epic Battle Fantasy IV.

Hime's theme from the Suguri series... Ok, when I think about it, this might be my favourite theme. Good thing I put it at the end of my playlist, huh? XD

Well... that totally wasn't me just recommending a whole bunch of soundtracks while sidestepping your question...

https://www.youtube.com/watch?v=TnLAC5AJPuM
THUNDER FORCE IV - Lightning Strikes Again

https://www.youtube.com/watch?v=jT4A-MSQgoI
Grim Fandango Soundtrack- 'Companeros'

Akira Yamaoka and his works for Silent Hill
Those are my favourite
Promise
Waiting For you

Bully
Neotokyo
Disco Elysium
Pathologic 1 +2
The Void
Blade Symphony
Smash + Grab
Gremlins Inc electro swing type thing going on

This is the police 2 - lightweight
(is an exception, the rest of the ost was boring, it really surprised me all of a sudden towards the end of the game)
https://www.youtube.com/watch?v=x7BE3YwtkUw

(The crew 2 ost is extremely generic compared to The crew 1)
The crew 1 - introductions (official ost)
https://www.youtube.com/watch?v=6tFkdufZ6UI
The crew 1 - A2B (official ost)
https://www.youtube.com/watch?v=K0AsTvJysoQ
We cry diamonds - i like it (in-game radio)
https://www.youtube.com/watch?v=g-4UpCJ0a1c

Moonlighter - botanical brigade
https://www.youtube.com/watch?v=5YRUPZpPYVM

(i like the hotline miami track you linked)

Tears by Health for Max payne 3
The Catalyst by Linkin park as credit song for Medal of Honor is also great fit seeing how game ended.
Honor for all from Dishonored

Undertale Asgore. I listen to this remix of it often:

https://m.youtube.com/watch?v=COwC0F6wxbU

But the reg version is also excellent ofc.

This one is nostalgic for me because its the first videogame I've ever played Supaplex and spent months trying to finish as a kid, good memories.

Some more old school jammers.

Amiga 500 - Enemy, Tempest of Violence Intro
Tokyo Twilight Busters (PC-98)
Dune - Arrakeen Palace

Some more recent good ones

Vampire Survivors Soundtrack - Mad Forest
The Toxic Avenger - My Only Chance (from Furi original soundtrack)
Low Roar - Don't Be So Serious from Death Stranding
Olivier Deriviere - The Streets | Streets of Rage 4 Official Soundtrack
M.O.O.N. - 'Hydrogen' [Hotline Miami Soundtrack]
God of War

I love how OP is checking out every single link, that's great.

I would usually say "all of Chrono Cross soundtrack" but since I'm limited to one tune alone, I'll go with this one from Bloodborne

My favourite probably won't surprise anybody.

Honorable mentions:
The whole damn Harry Potter & the Philosopher's Stone game ost.
Two Worlds menu song

lots of good musics and games!

one I remember very well is The River by The Bombay Royale for Far Cry 4. Still remember the mission I was doing at the end while playing it!
https://www.youtube.com/watch?v=sX6zNpK_n1I

Dont do this to me... whenever someone opens a topic like this, my mind falls into an endless rabbit hole. This in and of itself is a good thing, because it means videogames provided us with numerous memorable musical masterpieces troughout the years and its not falling on deaf ears, but on the other hand, there are too many to make a perfect, all-inclusive list. Leaving anything out feels like injustice of extraordinary magnitude so like many others here, I cant just choose one particular song.
But to actually provide to this topic, I will link some songs/ost that were not yet mentioned:

• Warhammer 40K: Mechanicus; This is something else entirely. If someone beforehand ever told me that some genius comes up with this "space-gregorian music with electric beats", followed by a freakin pipe organ and I would actually love it, I would have never believed them. Yet here I am. :D Very specific soundscape for a very specific theme. There is no way this could have been nailed any other way!
• Homeworld - Adagio for Strings; Yeah, while this is not an "original" per se, many may remember it from the movie, Platoon too, but this iteration from Homeworld really hit differently. The choir is just... angelic. I am not even religious, but even to me this music sounds like pure, holy blessing. Sad, but incredibly beatiful. BTW, the Homeworld soundtrack in and of itself is great too, with outstandingly unique atmosphere.
• Alan Wake - The Poet And The Muse; Lore and story woven into an in universe song. And a good one at that! Do I have to say more?
• VA-11 Hall-A - OST; The whole thing as it is! I have a soft spot for synth and the relating retro-futuristic vibe! :)

I will leave it at that, otherwise my whole week would be spent on naming countless other songs.
Videogame music is just too rich at this point, too full of insanely good music. Of course, I could have mentioned many that was already written in the comments. I also love the music in Celeste,A Hat in Time, Nier;Automata, Deus Ex, Elder Scrolls, Witcher 3, old Blizzard games (War3, SC), the Ace Attorney series, in every game of Supergiant Games, the Pokemon and Persona series, Metal Gear Rising, Final Fantasy, several visual novels... and also lets leave Touhou games and it's fan music scene as just a honorable mention, because that in itself is another rabbithole. I am in too deep, believe me. Like a whole another pocket dimension in terms of amount and quality.

I just played not for broadcast recently so that's what stuck on my head right now.
Pieces of my heart - https://youtu.be/kMApqjMn2YA

I was most impressed with Bastion ost
have One from it

and because of one of game trailers I like the most
This War trailer song

Dragon's Dogma - In the Crucible where Droplets Gather, I Wait

Besides the ones already mentioned, like Deus Ex or Life is Strange, I have to quote the theme from Journey

https://www.youtube.com/watch?v=TLfj3pAlrs4