Before I review this, you should know two very important things.
1. I am a total Gaiman fangirl. There are very few things he's written that I didn't love, and I look forward to a new Gaiman book more than I do to Christmas. Or my birthday. I have at least 3 copies of every Sandman book (My beloved originals carefully put away, digital copies, and the reprinted hardcovers :)
2. I live in Viking Central. I mean literally. It's 20 minutes by boat to Birka. There are more viking ruins (if you include runestones) within 50km of where I live than the rest of Scandinavia put together. My kids learnt to read runes at school, and there is a Viking festival here every year on the beach about 5 minutes from my house, where everyone comes and literally lives viking style for an entire week (of which my favourite part is the horses and the silversmithery, because mead--actually not that good.)
In any case, despite not being born in Sweden, I know the myths inside and out, they are still considered a really important part of history and culture in this particular area, and I've sat through many (many!) a school play where my kids acted one or more of them out. And I know how deeply funny most of them are, all the little subtleties that are often lost in translation. Like how Thor is dumb as a box of hammers, and Loki is ... well just Loki.
The result is, I actually wasn't, for once, looking forward to this book with my usual joyous anticipation, I was terrified slightly worried my beloved Mr. Gaiman would get something wrong, and I'd be horribly disappointed.
So to the actual review. You knew I'd get there eventually :)
I wasn't disappointed. Not in the slightest.
Gaiman takes some very fragmented, and occasionally contradictory stories, and manages to weave them into a coherent and totally readable saga, beginning with the creation myth and ending with Ragnarök, and detouring into all the funniest and most fun stories in between. While each story stands well enough alone, there's a master storyteller steering the whole thing along a red thread of narrative.
And of course it includes my absolute favourite stories. Including my two favourite stories: The one where Loki is the mother of Odin's horse and the one where Thor cross dresses as a bride. And people think the Marvel universe is so daring for having a female Thor. The vikings have been there done that, 1500 years ago :)
So, despite all the buildup, that's my actual review: It's great.
If you love the norse myths already, this is a perfect little compendium of the best of them, all in one little package - and if you don't, it's also a perfect little compendium to get to know them from.