The login screen music... always helps me when I'm feeling down.

Whitespace Swarm, Whitespace Ambient and Somber

I really enjoy listening to "Noxious Descension", I don't know why.

There's also "Lichen to a Polyp", "Two Slimes are better than one", "Roar of the Munitions Factory" and "Buzzkill".

I have some favorites for certain.

Main theme is pretty bland for a name but one of my favorite songs. Construct (Around the Clock Workshop), Blast Network (Krogmo's Got A Short Fuse), and pretty much every boss theme in the game, including the unused original Boss 2 song.

If anyone's got some free time and really likes the battle/boss music of the game, I made a little compilation a while back of all the main battle/boss themes along with some visuals: https://www.youtube.com/watch?v=R9VeGk6fO80
Can use it as either background music or a fun watch! I like to throw it at people when I'm explaining what Spiral Knights is, as although it's a lengthy video it kind of encapsulates the general feel that is Spiral Knights.

Sky Island Skirmish is my definite pick for best song in the game, and I'm not sure if I'll ever be convinced otherwise.

This track just feels special to me; the darker tone it seems to have compared to normal combat music while subsequently fighting an enemy that seemingly can't be beaten yet just makes me want more tracks like it.

Fangel's description is really compelling. I imagine. For other people. But not me.

I'm a player who turned off the game music about 10 seconds after launching the Spiral Knights application in April 2011. I like to listen to my own music, whether it be rock, hip-hop, jazz, baroque/classical/romantic, or whatever (or nothing). But everyone says that Spiral Knights has a strong soundtrack.

In which scene of the game am I most missing out?

To put it a different way: Which scene is ho-hum ignoring the music, but really amazing in how the music complements the rest of the content?

For example, as an outsider I would guess that the Arkus battle has special, poignant music. But nobody's mentioned it, so maybe it doesn't. If that's the case, then Arkus is an anti-example of what I'm asking for.

In which scene of the game am I most missing out?

I would say the Collector's original boss fight early-game is heavily enhanced by the presence of Unforgiving Onslaught when you first play through the game - probably the first time you'll get to listen to the song for long.

The song itself isn't special, but it certainly makes the fight feel like it is, and the deep, slow, slightly mechanical-sounding tones you hear throughout compliment the environment excellently.

-----

I don't actually remember what theme played during the battle with Arkus. I'll have to replay that sometime.

Edit: That would be Buzzkill, as mentioned below.
It definitely sets the theme for the fight, but it's also fairly toned down, and feels more like a background ambience than a truly epic song.

Am I the only one who things Sky Island Skirmish is the best song in the game?

...oh

Thanks for the recommendations. I'll start doing some targeted listening. :)

The Spiral Knights soundtrack is really something special. I don't really listen to much music, and am quite content sitting in silence most of the time. However I do enjoy listening to game soundtracks (primarily Spiral Knights, Payday 2, Undertale, OG Binding of Isaac). Spiral Knights is one of those games that sets its themes very well. Artistic direction for visuals is amazing, sound and music design is wonderful, story elements are present yet they don't get into your face too hard, actual gameplay is smooth and very satisfying, etc.

While the common background music is nothing to write home about (clockwork tunnels, status variants), they do fit their environment. One way to see this is to play through a candlestick keep with the music on - prior to the new music being created, it played the same music as a graveyard, which made the place seem ominous, slow, and spooky. With the music change to its current song, it turned the levels into a fast paced panic where enemies are flying all over your screen and you're constantly in danger of being bit by the grimalkin. The levels themselves didn't change, just the music did, but this change alters the entire player perception of the levelset.

I've just heard Whitespace Swarm for the first time.

I still stand by my statement that Sky Island Skirmish is the best piece, but...

DANG.

That's some rockin' beats right there

(...that sounds so stupid)

Try reading over the end of the Dreams and Nightmares dialogue with Parma's scout, but slowly and with the music flowing through. It's a perfect antithesis to Whitespace Swarm - if you listen hard enough, you can even hear the faint noises of the swarm echoing in Sanctuary's music, which further emphasizes its location.