I just don’t like Granny Weatherwax that much as a main character. She is, first of all, a leader who does not know how to lead. For someone who is described in the text several times as someone who has a phenomenal grasp of “headology” (psychology) she doesn’t really seem to know that much. She doesn’t know how to negotiate with people, she just knows how to manipulate them from above, and in any realistic situation that should present a number of difficulties, but they simply never come up in the books.
Ever noticed how conservative (in a very British nanny sort of way) Terry Pratchett is? Several of his protagonists have “practicality” as their chief virtue. I didn’t mind this in Sam Vimes, because even though he grumbled a lot he always seemed genuinely nice to most people. But with Granny Weatherwax all her kindness is off-stage: this is even lampshaded in the book, when Magrat is complaining (with some reason) about her, Nanny Ogg reminds her of all the nice things she’s done, which we don’t actually get to see.
I re-read “Men at Arms” yesterday because I didn’t want to continue with Maskerade (or study), and the more I think about it, the more Granny Weatherwax seems almost like the anti-Vimes. She bullies everyone else; Vimes gets bullied more often than not, although he finds ways to deal with it. She knows what other people are thinking but doesn’t seem to know herself particularly well; Vimes is exactly the reverse, although in a less extreme way. None of this is necessarily a reason to dislike the books, of course… I think my biggest problem is simply that I’m (yes, still) too fresh out of high school (which had many similar characters, different only in that they weren’t as smart and couldn’t do magic, thankfully) to be able to appreciate a bullying old woman as a central character.