People like to say it "To Aru" or "Toaru..." I don't think it matters, time to review...
Toaru Kagaku no Railgun is somewhat a "spinoff OVA" of Toaru Majutsu no Index (Which will continue sometime soon.) Only in Railgun, the main hero is Misaka, Mikoto, the level 5 esper of Academy City. You will see rare pop-ups of Kamijou, Touma, the main hero of Index, as well as Index herself (on top of the other Index cast) in the show. The main cast consists of her dorm friend and Judgement member, Shirai, Kuroko, who is also a practical lesbian towards Misaka, although Misaka disapproves. Uiharu, Kazari who is Kuroko's Judgement colleague and friend. And Saten, Ruiko who is Uiharu's friend and classmate. Saten has a habit of liking to flip Uiharu's skirt up for fun.
Before I talk about the story, there are 6 official esper levels, and 0 counts as a level (0 being the lowest of the low.) Saten is a level 0 esper and Misaka, like I said before, is a level 5 esper. She's is also dubbed the "Railgun" due to reputation for for electric attacks and level since there are only a rare amount of level 5 espers in the city.
Anyways, the story starts out pretty simple. Knowing the life out Misaka, Mikoto away for Kamijou, Touma, even though you might see him in the show. See Misaka deal with Kuroko and her antics. See Kuroko work at Judgement, which is kind of like an esper police. Then when everything gets settled the actual story starts to unfold. Unlike Index's plot, Railgun's main plot talk about the problems with espers and AIM diffusion fields. That's all I'm going to get into from that, watch the show if u wanna know more. xD
Unlike Index, Railgun really improved on staying on story and keeping the audience in suspense. It really felt like a detective show more than an action show (of course it had your average comedy and drama.) If people are expecting a straight action show, then stop doing that. It's like your expecting Misaka to be like Touma. No two people are the same. The show was great in it's own way. Some people thought it was better than Index. Some people thought it was horrible. Whatever. I thought it was great and I hope they continue spinoffs like these. I give it a 4.1 out of 5.