I've made it pretty obvious before, but I'm a total fan of Index...even if it is flawed....really flawed at that, ok fine it's a guilty pleasure! As such while I was excited about the film I wasn't expecting anything grand but a good popcorn action flick and for the most part I got what I wanted...for the most part. Basic synopsis this time is...well...Touma meets an Idol, and in usual Touma fashion gets in the middle of some pretty serious shit, where the ultimate solution is punching someone in the face in GAR fashion.
The story is pretty simple but for the most part moves fairly smoothly, especially the opening scene which really got me excited for what I was about to watch. However the middle part of the film may feel like it meanders a little especially since the movie is trying to have as many characters make a cameo as possible (except for you Hamazura, better luck next time). Then it reaches the third act where the pace really starts to pick up, much to it's determent however. The final confrontation wasn't all that impressive due to over saturation of characters involved and the rushed feeling of it all, and the plot twist at the end of the film winds up being confusing, if not rage inducing (due to being a fan of the light novels themselves).
Despite that however the film wasn't that terrible one of the best things about the film is just how well it looks. This is Index with a film budget (which apparently gets transferred to Railgun almost seamlessly.) and when the action scenes arise they are really fun to look at, as all action scenes of this franchise should be. Depending on how well you liked the characters before, it'll be a pro or con to know that they all act in character as a result of the light novel author writing the story himself, and for me it's definitely a plus (except for when Kuroko has to show up). As for the movie original characters the only two you really need to pay attention to are Arisa and Shutaura. Both characters do their jobs and fill their roles but are nothing extremely noteworthy, while I find Arisa likable enough (it's a relief when these types of characters aren't annoying) I think Shutaura has the stronger character overall. There's another character too but she's just a pawn in the overall scheme of the plot whose fate may get a laugh out of you if you are sadistic enough. There was potential for her to be a more interesting part of the movie but oh well, sour grapes. Music for the film was effective as usual and featured mostly remixes of tracks used throughout the series and contains a few pieces of it's own which sound great but depending on your taste of music probably won't stick in your head for many days after.
Here is the important thing to note: This is a film for Index fans. If you have no knowledge of he series before hand or are just a fan of railgun, there is little point to watching this movie, especially due to how simple the overall story is and numerous amounts of character cameos and continuity references and jokes it makes. That all said, speaking as an Index fan, I thought the film was fun. Flawed, yet fun. For someone who not only liked the first 2 seasons well enough, but is also a fan of the original source material it was nice to see these characters get a feature to themselves, it only falls short on execution near the end but the creator himself said that he basically wanted this film to be like 'a festival' of sorts to celebrate the series being around and popular for 10 years and on that end, I feel he succeeded.