Odd and the Frost Giants by Neil Gaiman
We listened to this on a road trip, and it was perfect for all of us. It assumes no knowledge of Norse myths, and is a completely new story - not a retelling of an existing myth (at least, to the best of my limited knowledge) - so it is enjoyable whether you've ever heard a Norse myth or not. If you have, there are subtle allusions to the myths which add to the feel of Gaiman's story being one of them: Odin's only having one eye, Loki taking animal form, Freyja being the object of the giants' desires.
A simple coming of age story, this short novel has left me wanting to read more by Gaiman. I'd not read any of his books before, but I'd seen episodes of Dr. Who he's written. I'm already looking forward to listening to another of his children's books on our drive home, and maybe checking out an adult work after our trip is over.