If you haven't seen the movie The Prestige, then you should not read the notes behind the cut. Really. However, you should know that the movie is based on a book of the same title which won a World Fantasy Award, and while events diverge a fair amount, the book's shelved in fantasy for a reason.
I quite liked the movie, which is a little odd for me because I usually don't like unhappy movies and this is a tale of obsession and distrust. I think it's the pleasure of its construction.
I found it a bit too long or slow; towards the 2/3 mark, I was saying, "Okay, we've gotten through everything else that's been promised to us, just get rid of the wife and then get to the reveals already." Though the structure did have this unfortunate effect, on the whole I think it was essential to playing fair with the audience. I was only confused about where we were in time once, when Borden met his wife, and that was soon cleared up.
Now, I have read the book, and I remembered what the two tricks were—but I misremembered which character went with which trick. This was, to say the least, unfortunate—and the misdirection about Tesla and the double who betrayed Angier kept me confused for a while. (I was thinking that the double might be a real twin who was an even blacker sheep or something. Hey, I was tired. And who would figure that in a movie with Hugh Jackman and Christian Bale, Bale would turn out to be playing the better character?) As a result, I knew what the opening shot of the hats meant, but a lot of the clues didn't click for me until afterward, like the child asking Borden "what about his brother?" after the bird trick and the look on Borden's face.
The movie did a nice job of importing some epistolary flavor through the dueling diaries, which is a hard thing to do on screen. Two of the biggest changes resulted from removing the framing device of the book's epistolary sections, though, and I think these were sound decisions.
The movie restricted the events to the lifetime of a single generation, rather than the multi-generation feud of the book. Since I think the movie already was too long, I fully approve. As a result, it had to ditch the revelation about Borden's child, which Chad recalls as being the following: in the book, Tesla's machine created inanimate copies of living things. Angier used the duplication machine on Borden's son, and so the inanimate copy convinced Borden that his son was dead. Angier then raised Borden's son as his own. At the end, Borden's son finds the "prestige materials": Angier's duplicates and one of himself. Which is a pretty creepy scene even if it lacks a logical reason for the duplicates' perfect preservation.
[Edit: see coffeeandink's corrections in comments below.]
The movie changes this to a single-generation story by substituting the creepiness of swapping a dead child for a live one, with the creepiness of killing yourself over and over again hoping to frame your rival for your murder. It makes the duplication a complete one, including consciousness, which makes the disposal of the duplicate far more disturbing and indicative of Angier's complete obsession, as well as allowing for the murder frame-up (even if the inanimate prestige materials were dropped in the tank, I don't think there would be water in the lungs to indicate drowning. Of course the movie also changes it so that the duplicate is created outside the machine, rather than inside with the original moved some distance away.).
The movie still raises the possibility that Angier will take Borden's daughter (interesting change there; girls are more vulnerable, women are the pivot-points for the rivalry, perhaps both), but I think it's a fair reading that it's this possibility that leads to Angier's defeat. Until this point, direct attacks had been confined to the magicians and their assistants. The audience is clearly meant to see this threat to a child as the last straw—a distraction from the very last straw of the repeated self-murders—and appears to motivate both Borden and Cutter to act against Angier.
(Is there any significant to their names being ABC, do you think? Cutter is a composite character for the movie.)
One could say that the movie is more pat than the book, since it has a clear and reasonably just resolution. That's not unfair, but I think it flows pretty naturally from the constraints of the medium—which is to say, a resolution now rather than later, and they could only hang one of Borden.
One could also say that the movie is anti-fantasy: there is magic, which is worse than the illusion. (My note to those who haven't seen the movie or read the book was because a number of reviews thought that Tesla's machine was cheating.) I think there are two things that can be said about this. First, the magic isn't intrinsically worse, it's what was done with it. Second, there's a comment in a Terry Pratchett book somewhere about how conjurers are more interesting than magicians, because conjurers are putting effort into it—which is related to several characters' comments in the movies that no-one wants the stage tricks to be real. I can see how some people might be bothered by it, but I'm fine with it.
- The water tank can't have been the tank that Angier's wife drowned in, since they were using a new tank every night and couldn't know when Borden would take the bait. Even if such an item would be reused after it was broken open, which I doubt.
- Showing Edison's men burning down Tesla's house was unnecessary.
- Angier's dying speech was not very comprehensible.
- Angier had a lot of faith that his theater was inviolable, to consider it the safest place for all his dead bodies.