Excellent movie. It is indeed as surprisingly gripping as it was said to be. I did have the ending figured out, although I didn't guess the exact mechanism. But the story itself is awesome. And you have to respect the balls it takes to make a movie about magicians after Will Arnett ruined them forever.
I'm not a huge fan of the "two people obsessed with the other's annihilation" genre, but this one's basically the ultimate mano-a-mano film. It doesn't quite treat the competition as a sideshow, but it certainly concentrates more on what drives the two magicians, their weaknesses as men, the sacrifices each makes in order to beat his opponent.
I do have one beef, which is that the finale could have been absolutely devastating, whereas in reality it was more of an "ohhhhhhhh, so that's how it ends" situation. There was no shock, no WTF?!?!? element to it. (I did figure it out, after all.) I think that's a result of the fact that both men abandon morality in the quest for ultimate supremacy, and thus give us paired antagonists, or at best a de facto protagonist, rather than a true protagonist to whom we can connect ourselves as an audience. It makes for a hell of a story, but it also deflates the power of the ending, because we're detached observers instead of invested participants. We aren't rooting for anyone... we just want to see how the trick turns out.
Still, it's a hell of a trick.