First off, I found this a reasonably easy read, with short chapters and a plot thats not too difficult to keep track of. The only exception to this being the Icelandic names of the characters (plus the various place names) - I would never claim to be fluent in Icelandic, so I'm glad I don't have to read the book out but really thats a small issue. I liked it as there's more than one story at play - there's a sort of fictional historical story (not that its set primarily in the past but it talks about Christopher Columbus' presumed discovery of America and questions whether Scandinavian's may have actually discovered America before Columbus) as well as the contemporary crime story. There's an authors note following the end of the main text, at the back of the book, which clarifies what is fictional and what has a true historical basis.
I was interested in both parts of the story (sub plots) and I liked how different chapters move the focus from one character (or set of characters) to another. I found myself being left guessing what may happen next and being proven wrong. At one point I was suspicious that I may have guessed who had committed the crime but then I was proven wrong within a few pages of reading on and that left me even more keen to read on and find out what the ultimate outcome was.
Also, as far as the crime element is concerned, it isn't horrendously gory or violent in terms of descriptions etc., which was good for me as I can be a bit put off by books which are especially gory. If you like Scandi crime noir type shows then this may be of interest to you and I'd say its worth a read. I believe the main character, Magnus, has been written about before and I hadn't read any of the authors' previous novels featuring him but I found it (as I say) easy to follow the story and get an idea of who the people were, obviously including Magnus, so I wouldn't say it should put you off reading it, if you haven't read other novels featuring Magnus before either.
I felt the ending was a little unlikely - you may need to suspend disbelief for the very ending - the last 10 pages or so at least. Also, I noticed the quote on the front cover which reads 'One of our finest thriller writers - Daily Mail'. Well, I wouldn't (personally) categorise this as a thriller read as such, as it isn't especially action packed or fast paced as such. I'd say crime drama (with a bit of history) is a better description.
If it interests you, I'd say its worth a look but its not a particularly amazing or memorable book (many books aren't) - its a good quick-ish read all the same though.