I think a lot of the recommendations were made in despair of finding anyone quite like Pratchett. Humorous fantasy is very hard, because speculative fiction has to take itself very seriously in order not to collapse into parody. Not many can pull it off for long; TP does. My recommendation was not so much as being "like" Pratchett but more along the lines of "if you liked this, you might like..."
I enjoyed Piers Anthony's books for a while. They got to be too much the same. Then I read an interview that totally put me off him... I actually don't remember exactly why; it was a long time ago, but that was the end of my interest in reading him.
I enjoyed the Gormenghast books, but I wouldn't say there' much (any?)humor in them, just weirdness. Dark, gloomy wierdness, but interesting reading. Wordy and bombastic, yes... keep in mind when they were written, and Peake was apparently going for a retro style even then, for the mood.
I had the same reaction to the Thomas Covenant books as some reported upthread. The author was too self important (I often feel the same way about Arthur C Clarke) and the rape was too much. I know it was allegorical but IMO that's no defense; I generally despise allegory anyway.
-Glenn