I came into this series expecting a Nasuverse-esque
setting; a highly-detailed constructed world with lovable, complex characters. To sum it up in a short phrase, it's a hit and a miss.
Toaru Majutsu no Index
has so much potential in its setting and plot, but settles for a mostly mediocre execution.
The main problem with this series is that it introduces so many characters, but fails to develop a good number of them. The most glaring example is the eponymous character, Index, who becomes nothing but an open target in the later novels. The fifteenth novel introduces so many factions and characters who just get thrown away for the sake of plot. And worst of all, some of the character development just feels out-of-place and unnatural; the direction that their characters take is just jarring compared to their original personalities (Accelerator and Mugino are the most glaring examples).
The narrative also leaves much to be desired. When the narrative settles for jarring descriptions of the female body interspersed with action scenes, or when the characters just dump on you pages of exposition, you know there's something wrong.
This is a novel that, I believe, is better suited to an animated format, but unfortunately, the problems which permeate the novel get translated into a different form in anime. The anime favors fanservice and cutting down/downplaying much of the interaction between characters. The first season did not have too many glaring problems, but the second season somehow got worse in terms of direction.
Not to say that there aren't any good points; like I said, it has a rich setting with diverse characters and interesting use of superpowers, which is why it's all the more unfortunate that it doesn't settle to become better than what it is right now.
, in my opinion, is great if you want to just sit back and enjoy sci-fi/urban fantasy action. However, if you expect it making full use of its setting and characters, or if you expect it as an example of a great story, then you will only be disappointed.
There is, however, some hope. The New Testament novels seem to fix some of the more glaring problems with its story, and there is still hope for JC Staff
animating the remaining novels in a better manner. Until then, these problems will stay with Index