The main problem of Railgun's Part 2 is that it wasn't in the manga (Railgun's source is a manga, contrary to Index which is a novel). The story itself was suggested by the author and made canon by being referenced by the manga itself... but seeing as it was only 'suggested' and not written by the author it suffered a lot.

Index's second half, on the other matter, is the author's complete problem. There are good novels and weak novels. The 2nd Novel (Himegami Aisa), for example, is the one most disliked by fans... to the degree of being ignored on the manga conversion.