As a big fan, I think the Vadim Jean adaptions (by "The Mob" films, in case people aren't sure what we're talking about - Hogfather, The Colour of Magic, and currently Going Postal in production now) are.... well, bad, really.
They have the LOOK perfect, and there's lots of great inside jokes and tiny detailed stuff from the books for the fans.... but the adaptations fail mostly because of poor casting (on the whole) and very poor direction. Hogfather's Part 1 was a complete mish-mash of plot threads that I'm sure would have confused anyone who hadn't read the book, and The Colour of Magic just didn't work mostly due to the casting of the two main roles - David Jason could have made a good Rincewind about 25 years ago, but not now. Sean Astin is a great actor, and he did well with Twoflower... but Twoflower is supposed to be a parody of an Asian tourist, not an American one.
Anyway, if it gets people interested enough in reading the books, I'll support them.
Having been involved in and seen many stage adaptations of the books, they work sooo much better on stage, because you can afford to be silly (to get audience laughs) and it's far easier to have a sixty foot dragon when it's all in the audience's imagination
[Best play to be in, and funniest to watch: Lords and Ladies. And no, I will never, ever be doing the Stick and Bucket Dance, ever again!]