A Certain Magical Index is the story of Kamijo Toma, a student in Academy City, and his fateful meeting with a young (looking) nun named Index, who has 103,000 forbidden magical grimoires memorized as part of the English Puritan Church's war on sorcerers. He becomes her protector after a few harrowing battles against both foes and (unknown) allies, and sets off on an adventure amidst the underground war between science and magic.
- Wider array of stories. Whereas 'Railgun' focused on a pretty narrow story arc for its entire first season, 'Index' has at least 4 distinct story arcs. One of which is the 'Sisters' arc, which is really the best story in the franchise. While less time is spent on each event than with the equivalent in Railgun, you definitely are not up against the same thing every episode.
- Self discovery. There's a major change that the main protagonist, Toma, goes through early in the series, that affect his development through until the end. Without spoiling, he goes from being a relatively normal, whiny underachiever to a brave, if uncertain, hero. And it's done in a way that you hardly notice the change.
- Necessarius. On first blush, the different factions in 'Index' can be a bit difficult to fathom. That said, the 'Church of Necessary Evil' has some pretty fun characters, like Stiyl Magnus and Kaori Kanzaki.
- Railgun! Yup, Misaka Mikoto's series spun off from this, so she's in it quite a bit. She's portrayed in a more adversarial fashion in this series (she's Toma's only combat in the first episode), but one could see that as being that 'Index' is from Toma's perspective.
- Everybody loves Toma. Seriously. Remember how in an earlier review it was mentioned about Ayato from Rah'Xephon getting too much play? Well Toma makes that guy look like the comic book dude from The Simpsons. Almost every girl in the show is into this kid. Just off the bat, this includes: Index, Mikoto, Komoe, Aisa, 9969 Misaka Sisters, even that holographic girl. And after seeing the second season, you can just throw Kaori on that list too! Only a few ladies seem immune, namely Kuroko (for obvious reasons) and Misaka 20001.
- Where did _____ go? Some cool characters simply disappear from the story. Stiyl vanishes for the last half. Kaori is gone for the whole middle. Even Railgun comes and goes. While in some ways this makes the show more realistic (no one sees all their friends every day either), it's weird for an ensemble show. Particularly since all of the people named are in the opening sequence!
- Wait, you're important? After being a sort of background character for the whole show, one of Toma's buddies becomes named and important to the story. And the other...doesn't. It's just odd.
- Subplots AWAAAAY! Oh man. There are so many subplots that just trail off here that it can make your head hurt to write about it. There are spin offs, a second season, and a movie to address a good deal of it, but really.
All in all, 'A Certain Magical Index' lived up to expectations. While Railgun characters are typically more preferable than Toma, all other things being equal, the variety of enemies Toma faces might make up the difference. Railgun has a better main character, but Index just has so much more story. That might give this one the edge.