Seeing Mr. Hugo's glowing review, I guess I'll give something by him a shot. Library Ho!
There's something in particular about Pratchett's homages that bother me. I don't know what it is, precisely, but I often get the feeling that he doesn't respect the original work very much. Maskerade was especially bad for that. I find myself wondering why he doesn't just write his own damned plot, rather than using his characters to upstage the originals.
In his defense, the entire premise of Discworld is built on satire, parody, and literary/historical references. I think my favorite part about his writing is that he's cultured and well-read, and it shows in his works. His writing is like an intellectual playground that he shares with his audience, full of ideas he's gleaned from a life of reading, learning, and living; and he wraps it all up in sharp wit and British Humor. In a few ways, I equate him with a modern Mark Twain.
Homages aside (which were heavier in his earlier writing days, *cough cough
FaustMort Cough*), he does tell his own stories with his own characters, and I tend to find his ideas worthwhile. I think
Small Gods would be my favorite work by him. Yes, the Ephebians are analogues to Greek/Renaissance thinkers, and the Omnian sacking of their Library was akin to the burning of the Library of Alexandria, etc. His fantasy world has its pieces taken from the real world (and what story, ultimately, doesn't?), but the story of Omnia and Ephebe, the conversations between Brutha, Vorbis, and their respective versions of the Great God Om, make for an interesting exploration of the dangers of faith versus theory, and knowledge versus dogma, and deals with it in a very even-handed way. Philosophers can be driven to use their knowledge to create tools of destruction and war. Zealots can be incensed by their prophets to do horrible things without questioning. Just the same, faith is merely a form of trust, and knowledge can make peace.
If you can dig past the silly trappings, he's got some good things to say.