So I've been watching A Certain Scientific Railgun T every week now. This left me in #Raildex mania mood. So after writing about the series and watch order I decided to write about the different themes each series take on.
There's a reason anime-only fans prefer the story of (the spin-off) Railgun over (the main story) Index. Some even pretend that the world is only compromised of the side shown in Railgun. (I disagree because the deeper you're in Railgun story, the more Index story events effect the world around Misaka Mikoto.) The animation and pacing is way better in Railgun anime than the anime of Index despite being made by the same studio that adapted Index Light Novel.
Part of that is because Railgun is adapted from a Manga that uses it's visuals to present a perfect mix of comedy and action, instead of a Light Novel that deals more with the psychological aspect of the characters, an aspect that's hard to present in an animated format.
The main factor that differentiates the two shows is the narrative style and the theme of each one of them!
The main story, A Certain Magical Index novels have the conflict between the Magic and Science sides as the main theme. That's only generally speaking however, as every volume is built on its own theme and provides its own conflict. The author notes of some volumes explicitly mention the theme of that volume. (For example the theme of Vol.2 is "Bad Ending" and Vol.7 a "Magic Book.")
The arcs of this story are short (as only the biggest arcs span more than one volume.) The styles of the arcs vary heavily from each other. Some arcs are adventurous, some deal heavily with mental issues and others are comedic. There are even arcs that are bloody and disturbing.
In a way (and I'm paraphrasing this guy here,) every volume in the novel is "its own movie" that ties together with the other "movies" to paint the world's bigger picture.
The casts of the arcs are always different. The main protagonist (Kamijou Touma) is the focus on the most of them as he gets in trouble and saves people lives quite often. But he's not the only protagonist of the series, and there are even arcs where's he's not present at all.
Putting that in mind, Index story is all over the place! You can love few arcs while hating others. You can love a character while hating an arc that focuses mainly on them, or feel the exact opposite! You can't know what to expect when you start reading a new Index volume. (Unless Accelerator is on the cover, then you can bet it'll be an awesome volume!)
Accelerator, the king of Anti-heroes!
So when a story like that gets adapted into an anime comes a problem! Index story arcs are very different and short that it's hard to make a good seasonal anime! The arcs that focus on a character's inner conflict without too much action are especially bad when animated. You can only show so much before the anime feel slow and motionless.
Novel Touma is an amazing character, Anime Touma is a bland character. What differentiates Kamijou Touma than other shonen heroes is the inner conflict he has when he fights strong opponents who usually have good reasons for what they're doing. He always manages to prove them wrong in the end, but the anime skips on some of the process to get there. Well, Several anime based on light novels suffer from this problem.
The anime adaption of Index tries to cram as many arcs as they can per season, and they faced a mixed results on how successful each arc was presented. Index III was especially bad as they tried to cram each volume into 3 episodes, removing anything unnecessary to the plot including the only (supposed) appearance of a fan favorite character.
So, for those who only watch the anime. Without the context of the novels, Index anime seems too ambitious and tries to start/end arcs too fast, both the pacing and the animation suffer for it, and when you have Railgun's style to compare to, you're justified to feel disappointed.
Railgun's manga on the other hand follows the adventures of only one character (Misaka Mikoto) and her closest friends. The main cast rarely changes, and the dynamic between them progresses in every arc. Focusing on a small group of characters helps to show many sides of each girl's personality.
The main four girls in Railgun's story.
Railgun's arcs are smaller in scope while rich on details. Most importantly however, is that every arc of Railgun (at least the Manga) is based on one theme and its evolution. Almost all the arcs focus on Mikoto's struggles with Academy City's Dark Side and her attempts to live a normal life with her friends away from it.
By the time of this writing, Mikoto has no knowledge of the Magic Side's existence in Railgun, and only became aware of it later in the Index Novels yet to be adapted into an anime.
The first three arcs of the manga (Level Upper, Sisters, Daihasei,) each feature one basic theme and they're all related. All arcs are connected by one scientist. (Unsurprisingly, a Kihara.) The last arc of the trilogy references the previous two arcs heavily. The current arc of Railgun T (Dream Ranker) features many parallels to the Level Upper arc while being the logical follow-up to Daihasei arc and picks-up beautifully from there.
Since Railgun's is a monthly manga and the anime catches up with the story relatively fast, the anime fleshes out some of the characters by adding slice-of-life elements between action. The first and second seasons add original filler arcs, that ties up some of the loose-ends each manga arc before them left unsolved. While these filler arcs are not Canon to the manga, some of the events in them are implied to have happened Off-screen.
This all adds to the coherence of Railgun story. Unlike Index story switches its narrative style every arc. (Sometimes several times in an arc.) Railgun always feels the same: If you liked the first few episodes/chapters, you'll most likely like the whole series.
If you asked a Raildex fan if they prefer Index or Railgun, if that fan consumes every content for the franchise (that they could get access to,) you'll most likely get: " The Light Novel is better!"
Kamijou breaks some illusions (NT Vol.4)
You see, those who read the Light Novel and are dedicated enough to read all the way through New Testament, are the people who're quite used to the quirks of the franchise. Index vs Railgun debate doesn't matter to them as much because every episode/chapter/volume only adds more to the lore. If you're a person who cares about the lore that much, settling for one side of the world won't cut it.
Of course, even Light Novel readers will agree that Railgun is better as anime. The question is whether they are think the Novels with their unique style or Railgun's manga with its consistency is better overall. You'll get different opinions depending on who you ask.
As for me, I only consider each series a part of a whole and while I prefer Railgun arcs over most of the Old and New Testament of Index Novels. Some arcs from Index are just so good that Railgun arcs might never get the top spot. (Also, Railgun as of yet doesn't have Accelerator as a main character, does it?)