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I loved this animation! After reading the book first, I totally agreed with how the characters were represented.

The three witches are by far the best characters, Magrat and Nanny Ogg are so funny. The story is good too. Taking elements from stories that have included witches in the past. In particular Macbeth and sleeping Beauty.I talked to Terry Pratchett online last year when he was doing a guest chat on yahoo. I asked him if he was happy with the two animated versions of his books

Wyrd Sisters and Soul Music, and he said he was extremely pleased with them. So there you have it. Some people may be put off because it's animation, thinking "It's for kids". Although there is nothing nasty in it to make it unsuitable for kids, I think it appeals to an older audience and that kids might not understand all the subtle and clever jokes. The books themselves are definitely aimed at adults.
Go and watch this now if you are a discworld fan.