Hypothetically let's say we've taken a record of Ihsahn's overall style from his past four solo records. Let's say this tome contains a fairly accurate description of the varying degrees of "black metal atmosphere" utilized on each of his records and there is an obvious pattern of progression from his straightforward Emperor-flavored 2006 debut of The Adversary to 2012's experimentally heavy, yet still identifiably Ihsahn, Eremita (lest we not forget the addition of saxophone beginning in 2010 with After). Now that you've had enough time and information to paint a mental picture of the tome, take a match and light the damn thing on fire. Why? Simple; Das Seelenbrechen is not what you're expecting from Ihsahn and follows no trend in his music.
It's also the best thing he's ever done.
While in the process of recording Das Seelenbrechen, Ihsahn pointed out that he wanted to go into the studio and just try to convey moods more than having a structured album set up for recording. It's an ambitious idea that's flawlessly pulled off in a multitude of styles, some of which Ihsahn hasn't explored in his previous records.
Sticking with the familiar, the songs "Tacit 2" and "Tacit" (in that order) start off with noisy distortion and disorganization that evolve into an organization of the previous sounds that grow and grow into a chaotic horn break and hellish sounding end, reminiscent of After at points. Songs like "Rec" and "Sub Alter" rely heavily on clean-ish guitars and plenty of driving atmosphere softly pummeling away, whereas "See" could very well be a Sunn O))) song (but shorter). Those are the closest you'll be getting to "traditional" Ihsahn, and they're a pretty far cry from even that.
You've heard "Hilber," which is quite doom-laden and foreboding, but where Ihsahn explores and succeeds with this record (aside from the overall success of the record) are songs like "Regen," "NaCl" and "Pulse," which find Ihsahn exploring almost movie-soundtrack-like areas of his sound. It's the incorporation of pianos, electronics, orchestras, and essentially everything that isn't your traditional metal band sound in the mix… and it's amazing. Haunting, of course, but amazing nonetheless. Even experiments like "M" are flat out amazing, where quiet spoken word all over a sudden gives way to a Pink Floyd guitar solo over an Opeth backing for a solid four or so minutes.
In essence, Ihsahn's Das Seelenbrechen is nothing you're expecting but everything you've ever wanted out of his music. There's no "complexity" that takes a few listens to "get" on this album or anything like that; one spin and you're hooked.