Wow, I haven't Newbery blogged in a while and I feel like a bit of a slacker. Time to plunge back in!
I'll admit that I had a bit of difficulty with this one. I'm not remotely familiar with Irish folk tales. I'm sure these stories are marvelous for those who are. However, for me, I felt like I was dropped into an unfamiliar world and left to fill in the gaps on my own. The book has multiple short stories all centered on Fionn, how he was raised, and his many adventures. These stories, despite being chronological, do not follow or build on one another, so don't need to be read in any particular order. This was not the book for me; I wanted continuity (you don't just introduce the son of your protagonist and then never mention him again!).
However, I did want to be fair to the book so I loaned it to a coworker who's a biiiiig iriphile (Eirephile?) to read over the weekend. As a former teacher she was pleased with its readability, and she enjoyed it because she was already somewhat familiar with the cast. So today's American kids probably need a bit of curriculum support to get into it fully, but it has its time and place.