The Fionavar Tapestry - the trilogy of which this book forms the last part - is clearly sub-Tolkien, and it's also in my opinion journeyman work. That sounds like a very bad beginning for a review - indeed it is - but this trilogy (and this book) is very far from poor work. It's close to the best fantasy available, and that, I think is why I'm inclined to judge it harshly. It just falls short of real greatness.
Why does it fall short? Well, for me there are a number of reasons.
Firstly, the homage to Tolkien is just too strong. It isn't surprising - Kay was the joint editor of the Silmarillion in preparing it for publication - but in my opinion it stunts these books.
Secondly, I find the 'Holiday from America' framing narrative just too corny. If you want to write a work of fantasy, fine, do so. If you want to introduce a group of characters who are foreign to the environment of the narrative (which is a useful device because it solves a lot of exposition problems) do so. But why, for heaven's sake, do they have to be dragged out of contemporary North America? It's presumably intended to add credibility to the story, but for me it does exactly the opposite.
Finally, what utterly sticks in my throat is that - as with Tolkien, as with so many other works of fantasy - the outcome for which our heroes strive, the ultimate triumph of 'good' over 'evil', is the restoration of an absolute, hereditary, pure-blood, patriarchal, male monarchy.
And yet despite all that it's good. Despite all that and less than perfectly rounded characters. The reason that it's good is Kay's extraordinary depth of knowledge of European (and North American) folklore, and his ability to borrow and integrate folklore elements from many traditions into a cohesive and compelling narrative. That, and the fact that he can write.
This is nothing like as good as Kay's later work, which for me is the finest fantasy available today. But it is still very good.