(One can always check out Wikipedia for more spoilers.)
Some have said that this movie packed too much into the limited time frame. But movies like these are so much more fun because one could realize new insights upon multiple viewings.
Those who think this film is like "Batman vs. Wolverine" probably are more into plot-driven movies than character-driven ones. And The Prestige is most definitely a character-driven movie.
Michael Caine's "Alfred the Butler" aura works very nicely to soften the cutthroat competition between the magicians.
Tesla, science, magic
I like the way Nikola Tesla is portrayed. I admit to partiality toward scientists and engineers... but only those with good sense and wisdom. Tesla is a curious character with quirks and a brooding contemplative tendency. Though in this movie, he's the brilliant mind with the voice of wisdom.
He builds a device that creates a double of the original in another location, be it living or not. He understands the implication of his teleportation-cloning apparatus and warns Angier not to use it, and knows that Angier would anyway. Here we have the scientist who must watch an inherently neutral machine get abused.
One can say that the scientist has a responsibility to prevent that, but honestly, some people can turn anything and everything into weapons. Harnessing the force within subatomic particles has led to radiation therapy and fission bombs. Same with dynamite, airplanes, genetic manipulation.
Science can be like magic when it's not well-understood. But even after it's well-understood, it can still be like magic. If one does not lose the ability to appreciate the aesthetics of the underlying mechanisms.
The magicians' rivalry is a positive feedback of ever-escalating obsession with perfection and maintaining the illusion of success behind their rather imperfect life. That's the ultimate magic trick. As Buddy Kane from American Beauty puts it, "In order to be successful, one must project an image of success at all times."
But what about the inside? What if it's just an emptiness? Like Borden/Fallon each living half a life and driving their loved ones to demise? Or their thirst for revenge veiled by constantly trying to one-up the other on the stage?
Twins who're in love with two different people while pretending to be the same person... just asking for trouble :-P