The primary value of this book is the illustrations, and the snarky tone Grant takes in describing the myths. I enjoyed it a lot, but I'm glad I'd already read some other works on the Norse myths, because this is definitely an "introduction"--the space limitations of the work caused everything to be reduced to the bare essentials.
However, this is an extremely valuable resource for the fact that it's the only work I've read that includes lesser-known details from the myths: Thor and Sif's daughter, the worship of Loki by the peasant classes, and so on. That was a huge appeal for me, and I recommend it on those grounds. Just, like I said, you should have a baseline for the myths beforehand: the prose edda, the D'Aulaires' work, or some other more in-depth collection.