I can count on one hand the amount of times any show, game, or book I've seen/read has shot up THIS much in quality between releases.
The animation is fine, but it was always, the music is great, but it was always. What Railgun S does is give you an intensely gripping plotline to follow that changes characters, alters the narrative of the world in a big way, and remains consistent in quality throughout the season. The cast of characters were...fine, I guess, in the first season, but I would have never believed you if you told me I'd be so attached to Misaka (the main character) and to be visibly panicking whenever something potentially dangerous was going to happen. I would have laughed if you told me that these writers could introduce a character at the beginning of an episode and have me fall in love with them before the episode was halfway finished. And I would have slapped you if you told me I'd be staying up all night line, binging episode after episode, because I suddenly couldn't put it down.
The show focuses a lot more on pure character and emotional moments, which works wonders, and the plot twists, reveals, and new introductions are all fantastic. The fight scenes are easily the best they've ever been; there was exactly one fight scene in the first season that I liked, but all of them here are great. There's a simple two-episode fighting sequence gauntlet where Misaka faces tough opponents one after another, and it reigns among my favorites battles in anime history due to the animation and soundtrack working perfectly with the pacing, dialogue, writing, and creativity employed.
There are also a few slice-of-life episodes sprinkled in, and each are just as good as the best of Season 1 and make for an excellent break from what begins to be a serious show. The new characters are fun and interesting. And the Chekhov's Gun that is Misaka's rival from Season 1 comes to a head and plays out masterfully, far better than I could have predicted.
There's a second arc after the first, main one, which isn't quite as good, but is better than any in the first season, and by some distance. It has lots of slice-of-life elements while filling things in with a suitably engaging plotline, wrapping things up from the last arc and acting as a sort of celebration of the series. I quite enjoyed it myself.
The season isn't perfect. There are serious pacing issues in some episodes, characters that were main characters from the last season are either seen rarely or never touched upon, and while it's lost a lot of its bad writing, childish humor, and ecchi-ness, those aspects do crop up again, albeit rarely.
Still, put simply, it rocked my world and made me invested faster than almost any other show I've seen. I only hope Season 3 is up to the task of following this one.
Also, Saten's little "kun" noises when she tries to sniff something is literally the most adorable thing I have ever seen.
