Disclaimer: The following expanded from pondering on an answer to VaSA's question, and should not be taken to express a preference for songwriters or a lack of appreciation for contributors not specifically mentioned.
I heard the song within about 12 hours of the album leak. Even in shit quality, I got it immediately. The hanging chords in the chorus, much like any given Amon Amarth song, are tributes to the natural fury that only northerners get. Typically, the fury of fimbulwinter; in the song, the flames that wash the world away. There's something about guitar shredding and double bass roll that reminds of razor wind, either in winter or on open water.
Sundin songs are very identifiable, even without writing credits, because they stand out so heavily from the writing that many other band members do (specifically, the Henriksson/Jivarp collaboration that pens the largest part of the discography on the most recent albums). While much of the core DT literature is fast-paced and focused on balancing the exploitation of powerful melodies with rapid, exciting transitions, Niklas' music is more classical and much more abstract.
Compare: Lost to Apathy, Blind at Heart, and Empty Me from Henriksson to Inside the Particle Storm, Iridium, Winter Triangle, Silence in the House of Tongues, and Star of Nothingness from Sundin.
Fiction and WatV both feature these really neat little instrumentals. While not a fair comparison to full-length vocal tracks, they do illustrate the point. Star of Nothingness moves through shades of melancholy, but it has a sense of movement to it. Winter Triangle need not even have the word 'winter' in the title; anyone who has ever ventured alone in midwinter night would immediately recognize the dramatic tranquility of the scene and the building sense of some looming "other" in the otherwise empty air. Silence in the House of Tongues, interestingly, is a miserable track, and almost certainly intentionally. The droning, dissonant guitars never move much in the song, but they drag the listener through their space. Some entertainment is art, but not all art is entertaining. This track communicates, but not a sentiment that you will necessarily want to hear daily; you probably have an abundance of your own misery to experience.
In the more developed songs, such as Inside the Particle Storm and Iridium, the same basic premise is extended. Rather than blast through multiple high-energy sections with an emphasis on transition, these songs feature longer sections, mini-movements in a classic sense, each developed to give the listener a sense of space. ItPS develops this lovely little groove, almost jazzy in its dissonance but a bit too menacing to be fun. The distortion drops in and lets you adjust to the new space before the slow chord changes of the guitars and synths shred every hope you had of getting some sleep tonight. Note how ridiculously slow the tempo is (for a metal song), and the number of words you can fit in a single line (Inside the Particle Storm, where clouds of napalm shiver with the promise of one final dawn). The song fades back into a melancholy clean section before rebuilding to it's chaotic crescendo. What's brilliant about this is the fact that that's not how modern music works, and is even fairly unique for DT. Changing it up in the middle is one thing, but dropping the drums to groove isn't done often. It should be noted that this isn't terribly uncommon for early 90's death metal (In Flames - Lord Hypnos).
I have nothing to say about Iridium that isn't already in the other thread, but in short: the chorus, and the verse-chorus transitions with the subtlety of a sledge-hammer to the groin. While the rapid transitions aren't exactly unprecedented (mostly I just want to share the
greatest ever recording of a brilliant piece of music), they are always bold, ambitious moves. Here, the dramatic power of the chorus supports the brain damage of the transition by breaking your heart too.
What makes the choruses of both songs work is the death metal intensity applied to every note. The melodies are slow, but calculated note-for-note to drag you along the author's intended emotional ride (See also: Arkhangelsk). The death metal textures, a mix of buzz-saw guitars, rolling drums, and keys (organs in ItPS and whatever it is in Iridium that makes me feel like my skin is melting (synthetic brass?)), make each note a sizzling gift of wonder. While the more rapid songs guide you from section to section, allowing you to sample flavors of energy and emotion, these songs strap you down and force-feed you a hearty broth of hellfire in a single section.
While composers tend to work in certain styes, note that Sundin's Shadow in Our Blood is actually more like the Henriksson/Jivarp-type songs than his other abstract, impressionistic compositions. The Mundane and the Magic, conversely, sounds like something that Sundin would have written, but it actually belongs to the other side of this comparison.
TL;DR: Some DT songs are written by ninjas who will emotionally flay you before you even feel their blades, others are written by a mad impressionist who will paint spaces on your exposed gray matter.