I've been listening to the audio for the past month, as narrated by Celia Imrie, but either my copy, or the production as a whole was so horribly done - 90% of the thing sounds like it was recorded from underneath a feather pillow - that towards the end I finally cracked and last night picked up my hardcover edition and finished it off.
That's not to say Celia Imrie did a bad job - she didn't, she was excellent (although her Nanny Ogg voice was too shaky and sometimes made her difficult to understand). If you're tempted to listen to this book on audio, and you see this particular edition, listen to a sample first and make sure you're edition is not muffled under a pillow.
As for the story - taken at face value, it was ok. But you can't take any Pratchett at face value, and the veiled subtext upgraded it, for me, to good (with bonus points for the mugging scene). I love Granny Weatherwax, and Nanny Ogg. I wasn't quite getting the appeal of Greebo, until the scene with the Fool - that moment where he looks down at the Fool from atop of his head was sublime, (and Celia did it perfectly). As for the Fool himself, I think I liked him more for having heard him narrated, than I would have had I read him from the start; Celia infused an intelligence in him I'm not sure I'd have given him, given the repetitious nature of his speech.
I think I failed to receive the characters of the Lord and Lady Felmut the way the author intended them. If satirically humorous is what he was aiming for, I definitely failed. These two just came across bitter, twisted and creepy - I should say Lord Felmut did; Lady Felmut just seemed to me a straight caricature. And since I'm complaining (not really) I'll add that while I loved the element of The Land, I wish Pratchett had not been quite so vague about it and it's connection to the throne. I understood it well enough but would have enjoyed it more with a tiny pinch more detail. And I understood the dynamic at the end, between the two brothers, until Granny, Nanny and Magrat got through with me. And how old is Magrat supposed to be anyway?
Overall, even though it doesn't sound like it, I did enjoy the story - it's Pratchett after all, and even his weak books are better than a lot of best efforts. I'm going to try Witches Abroad on audio too, because even though this edition's sound quality sucked, I think I get more enjoyment out of the stories when they're read by someone who obviously understands Pratchett's writing. But I'm definitely checking out the samples first.