I can finally say that I agree with you: I didn't like "Colour of Magic" very much either. Especially the part about the parallel universes where the characters have translated version of their own names and such.. It was just too weird and incomprehensible to be fun to read! But I hate to leave a book unfinished, so I read it to the very last page.
Moist, Pratchett's books are among the few that can actually make me laugh out loud
Sometimes because of the jokes, mostly because of his amazing style of turning around sentences so they become hilarious.