Not really a review, but I was asked for a opinion, so: I'm nowhere near a qualified scholar of anything Welsh; therefore, I probably missed a lot of intricacies. On the top of that, I read the translation that is generally viewed as inferior. But needs (student's ever-empty pockets) must, so free...
This is a very old series of legends. In fact, many of the stories have inconsistencies and some of the stories break off and end without explanation. (Even the footnotes admit that they are missing information.) While that is not the fault of the editors of the book (they can't just make up the end...
I have tried reading various translations of The Mabinogion, by far this is the easiest translation to read. It helps that the hardcover has two bookmarks, so you can read the notes easily as you go.As an introduction to these myths, this is a great place to start.
Welsh myths that provided the basis for some of the later Arthur stories.