I listened to this on audio as I love Kramer's narrating. That said, I got done in less than a week and it was outstanding! It was almost Elantris meets Harry Potter which was fine by me. When I say that, I don't mean to compare it to HP at all but for the school setting.
I was pretty bummed when Joel didn't become a rithmatist but like many others have said, you know he will. For 1, the shadow thing was there to "latch" onto him but i believe it was scared of the electronic coin? Didn't he have that with him? I am not really sure about that theory but clearly it wanted to make him a rithmatist or else it wouldnt have been there.
Either way it was kind of cool how it all ended and I definitely did not see all the twists and turns coming in play.