Disappointing. I expected this series of stories originally mentioned in the Harry Potter books to be far more engaging and to provide greater insight into the universe Rowling created in the HP books. To be honest, I wanted it to be just like an HP book, and it is far from that.
I think the clue we get is in the afterword, which describes how Rowling and some fancy Countess banded together to create a children's fund (which disturbingly doesn't seem to do any actual work, but is more involved in networking), and this book was written by Rowling so that its profits could aid the fund. A worthy cause, sure, and the book isn't expensive by any stretch of the imagination, but couldn't she have put a little more of her heart into it?
Instead we get decently written, but obvious, fairy tales accompanied by footnotes written by Rowling herself (dull) and annotations by Dumbledore (funny, but incongruous). The last tale does provide a tiny bit of information on why Dumbledore acted the way he did in the last couple HP books, but not enough to have made it worthwhile reading the entire Tales.