Yes, and I think part of the reason was because, well... there were no musical numbers and it was darker. Perhaps if it featured a couple memorable songs then maybe it would be liked more. I thought it was a good movie. Even if I did read the books.
And yes, I read all of the Prydain chronicles books and I do realize that they sort of merged the first two books together in a way, the "Book of Three" and the "Black Cauldron" however, let's also not forget that they tend to loosely follow most of the fairy tales they base their movies on as well... However, I love the movie anyways...