Ok, I just finished watching the last few episodes of To Aru Majutsu no Index, and I have three observations, two of which are spoilers (one speculative) and so I’m putting them below the fold.
First, the non-speculative: I was surprised that they ended it on a cliffhanger, with the next arc clearly set to begin. It’s an old trick to create fan desire for a continuation of the series, so it’s not that surprising; especially given that the series was a compilation of multiple light novels.
The big one is much more speculative: I think from a conversation between Aleister and Tsuchimikado and putting together other pieces (mainly how Imagine Breaker works against both magic and psychic powers), that Touma registers as a level 0, because he isn’t a psychic, and he can’t do magic because he isn’t a magician either. He’s something else, a fusion of the two, or a third way entirely, and Aleister Crowley, who is a mage of some importance in the city of science may have been responsible in some way for his creation.
At the very least, it’s obvious that, having discovered Touma, Aleister is manipulating things behind the scenes for his own purposes. He’s also probably the one responsible for getting Index entered into the computer system so she can enter and leave the city without alarm.
Oh, the third observation? Funniest. Parody. Ever!