I liked both mini-series, "Dune" and "Children of Dune". Of course, I come from the perspective of only hearing that the Frank Herbert novels are excellent, and not experiencing that excellence for myself (yet). Since I don't really have an original to compare them to, I thought they were good.
Someone made a comment about the bad acting in the first original... sure, it wasn't the greatest acting, but it wasn't the worst. I was able to suspend disbelief, and that is enough for me. Perhaps I have been desensitized because of all of the bad acting (and writing, and directing, and ... etc.) I've seen in student films here...
Anyway, I'll probably go to a bookstore and grab the books sometime, and read them over the summer.