Railgun easily stands alone from Index. Especially since it doesn't add magic, religion, and all the other things on top of science. I gives me something fantastical without overloading it too much.
Anyway, I watched a minute or two of the raw. Not too much since I didn't want to spoil anything before I could actually watch it subbed. I'm so into Kuroko's voice, I have no idea why. As soon as Kuroko came on I was so excited. She's definitely my favorite character.
The anime does a lot more for Saten-Uiharu than the manga. I'm up to current translations on the manga and their relationship is hardly seen. I like the liberties that the anime takes with it. especially since the manga and light novels act more as side stories to the "main" plot of Index, while Railgun the anime can stand on its own easily.