J.C. Staff (yes, THEM) did a great job with the Railgun series and created a very complementary side story to A Certain Magical Index which I think surpasses the original (particularly the second season, Railgun S). Mikoto Misaka aka "Biribiri" is one of my favorite anime characters and Railgun gets her front and center in the action, which is never a bad thing. I watched the first season of Index before this and I think that is the best way to truly enjoy this series. Railgun can definitely be watched without seeing Index first, but all the Touma (he is such a boss in Railgun vs in Index) cameos (and other characters allegedly) really lose their impact. And while Index was purely an action shounen, Railgun is more of a girly slice-of-life where the chicks also kick ass during their time off. This is particularly true of the first season which is about 50% SOL episodes. The second season is beyond epic and there are only a few fillers there.

The biggest strength of this series is without a doubt the protagonist, Misaka. I love her. There is so much to her than just a tsundere with unspeakable esper powers. But it isn't until the second season, where her character really gets a chance to develop and go through some truly difficult hardships. Shirai is hilarious with her yuri love for Misaka and Uihara and Saten are there to be cute adding to the girly SOL part of this series. I wish that there was more Touma in Railgun (like in every single episode) but when he does appear, he comes off so much better than he does in Index (so much less preachy). The action scenes are animated very well and give us a great variety of esper powers especially in the second season. The soundtrack for Railgun is fantastic filled with great BGM tracks. I loved the OPs and EDs from both seasons (especially Dear My Friend and sisters noise).

As I said earlier, the first season of Railgun is much heavier on the girly SOL. I didn't mind this that much but there were a few too filler episodes for my tastes. However, the second season of Railgun is epic and really cuts down on the filler. The first 16 episodes of season 2 cover the "Sisters" Arc which is hands down the best arc of the Raildex series and J.C. Staff knocked it out of the park. Even though Index covered it for a few episodes in the first season from Touma's perspective, Railgun really delves into everything Misaka had to go through especially her suffering and depression. I absolutely loved every moment of it, in particular the final battle, even though I kind of knew what was coming. The final arc is not as good, but I'll let it slide since the "Sisters" arc was so epic. So, I'd give the first season a 7/10 and the second season an 8/10 (a 9/10 for the Sisters Arc).

If you've watched Index at all, Railgun is a must see if you liked Misaka in any capacity. One can never get enough of Biribiri. It is definitely a step up in quality from the Index series. And you don't have to watch Index before this (or at all) in order to enjoy Railgun but it definitely helps. Anyway, if you like watching girls doing girly things and kicking ass with crazy esper powers, this is the show for you.