"Five favorite" seems to be the key phrase here. If you think of the Rolling Stone list recently compiled (some of which was downright embarrassing) you can see how that comes in to play.
Having said that, though, I will add that Pullman's "His Dark Materials" trilogy is a truly outstanding work. Ostensibly a children's story (on which level it functions very well, with loads of mystery, suspense, and memorable characters), the trilogy also touches on some pretty heavy issues (the nature of "Original Sin", scientific responsibility, sexuality, and conservationism just to name a few).
I would not say that they are great books in the same way that say Lord Jim or The Moviegoer are great books (in my own humble opinion), but they are most assuredly well-written, suspenseful, unusual, and thought-provoking.