I finally finished this book this week (I took a year long break somewhere around page 400) and it's left an impression but I'm still not sure what I think.
It's a book set during the Third Reich told from the point of view of a cynical SS officer - but not so cynical he still doesn't think there's still some value in the work that he does. And his work takes us from the Einsatzgruppen Death Squads, Stalingrad, Auschwitz and explores other dark places, including his extremely disturbed personal life - it's not an easy read. He meets several real life characters, famous and obscure, notably Himmler, Eichmann and the commandant of Auschwitz, Hoss.
There's not much unreliable narrator stuff going on actually, because he's not particularly repentant about his crimes despite obviously being scarred by them - the narrative voice is more like one of the downtrodden private investigators you'd get in a detective novel. It's especially interesting to explore the Nazi mindset from a perspective from someone who's cultured, intelligent, and has decided to incorporate it into their worldview and can argue to himself, or for the reader's benefit or both - why what he's doing is the 'right' thing, or at least no less unacceptable than what is going on on the other sides in the war.
On the downside - this book feels far longer than it needed to be. It's nearly 1000 pages long and without spoiling too much I didn't feel like the relationship with the narrator's twin sister or how things resolved with his mother were necessary in an already packed book. They ultimately don't really go anywhere important and feel like filler.
I really liked the lack of sentimentality in the book though, there's no attempt to make the situation better than what it was. It's probably not something that anyone would want to go through without some interest in the Nazi period; that said given what's just happened to Israeli and Palestinian civilians it's a reminder that the potential is always there for people in organisations to treat life as a cheap thing to be dispensed with if that's what their leaders say