And, uh, whoo.
Now, I'm perfectly aware that if you adapt a novel for movies or television, you have to cut a ton of stuff out just for space. But if your adaptation actually changes the theme of the work, you're doing it wrong. And they did it wrong.
Might as well start with the letters in the Post Office. In the book, the letters (which just piled up over time due to the postmen falling farther and farther behind, until they filled the Post Office to the very ceiling) simply want to be delivered. That's why Moist is inflicted with strange psychic visions and dreams whenever he spends time near them; the other postmasters died because they couldn't understand what the visions were. Although ultimately most of the letters are destroyed in a fire, Moist at least makes the effort to get them moving again, and this is an important part of his character development as he starts taking the Post Office seriously -- not for the sake of the letters exactly, but for the sake of the people who put their heart and soul into writing them -- and using his con man skills, not just to save himself any more, but to genuinely make the institution work.
In the movie, by contrast, this theme does not exist. Instead, the letters seem to exist solely to assist in Moist's personal evolution away from being a heartless con man: they trap him and broadcast little morality plays into his brain, showing his past misdeeds and how his "victimless" cons actually hurt innumerable people. (Oh, and it turns out the other postmasters were just killed by Mr. Goyle, the end.) Instead of Moist realizing himself that he needs to change, the lesson is just rammed into his head by external forces. Not only does it flush away a major theme of the book, it's also completely pointless, given that the whole rest of the story is also about Moist coming to grips with that. In fact, at one point Moist learns in great detail about how Adora Belle Dearheart's family was ruined by one of his cons, and five minutes later we are then presented with exactly the same story as told by the letters. Given, as mentioned above, that the space available in a movie is strictly limited, wasting it like this is just inexcusable.
...Especially when, and this is where the film takes an acrobatic pirouette over the shark and wins a medal, the emotional climax of the little morality play is learning that Adora Belle Dearheart started smoking because of her family's ruin, and it's all Moist's fault.
That's what this came down to? She started smoking, and that's the worst thing? That's what they're going with? Now yeah, yeah, it's a bad habit don't light up kids, but smoking is not the worst thing in the world. By the scale of everything else going on in the film it doesn't even budge the needle. But that's what gets the most emphasis. I distinctly recall a cry of "oh, come ON" echoing through my living room.
And speaking of Adora, they made a hash of her character, too -- especially annoying as she's pretty much my favorite female character in all of Pratchett. In the book, she starts prickly and, what is very important, she stays prickly. Moist does get on her good side by the end of the book, but it's not that the ice queen melts into some sort of stereotypical ooey-gooey simpering lovesick puppy; it's that she gradually becomes willing to trust in his positive intentions, because he demonstrates that he's worthy of that trust. She still remains the strong, practical, sarcastic person she always was. By contrast, in the movie she's just the stereotypical ice queen who warms up for no reason. This exposes another stupidity of the "omg, she started smoking" angle, too: the clear subtext is that Adora acts so deliberately unpleasant because of what Moist indirectly did to her family. But that's just not the case in the book; she mentions that her brother's childhood nickname for her was "Killer." She's always been that way. Not everything in the world is about Moist.
(Wow, there's a sentence I never thought I'd write.)
There are plenty of other complaints I could make. Mr. Pump playing Cupid to Moist and Adora is just absurd. Golems think differently from humans; they just don't care about that sort of thing. The opening scene where Moist is verbally jousting with his jailers, one of the best scenes in all of Pratchett, is almost totally eliminated. And I have a feeling they were going to make a mess of Moist's character arc in the second half of the film, too.
Pretty much the only good part of the film was Stanley and his pins. One can't help but point out that this is almost the only part that made it through from the book unmolested.