Granted, The Black Cauldron is quite a short book, but I still think it says something that I read it in two days, with a lot of other stuff going on in my life. Honestly, I can't even put my finger on what it is that makes me give it four stars instead of five... the absence of some intangible something. Nonetheless, a great book.
The Book of Three was fun but took awhile to get going, and only moved out of normal kid adventure now and then, but the second book goes into grander, more epic, and more mythological territory pretty much immediately--expanding the world, and doubling or tripling the cast just in the first chapter. Even though it was only 180 pages it felt big, and the world--even with its relatively short distances between places--felt huge.
The book also feels bigger and better because Alexander did not shy away from having dark and violent things going on: something I can always appreciate in a kids' book. There's fighting and killing and moral relativism and eternal damnation (of the zombie sort) and some suicide at the end for good measure. But, it never stops being enjoyable, and the supporting characters remain funny throughout. The Tolkien parallels remain, but bothered me even less (read: not at all) because of the great spins taken on them.
All told, great fun. I'm gonna read the whole series in a row now.