Saten was a good character, but she made a few bad choices in the anime. she should have stayed away from those dangerous people, and the whole level-upper thing. i cant belive she went ahead and did what she did. at least at the very end, she did some cool stuff.
as for me Misaka and Kuroko are my fav. i love how those two interact with each other.
Well it really helped build up the story (well, arc) so I thought it was all in good terms, besides, what Ruiko did was what most people would do, Railgun took a more realistic approach with the short sighted-ness and the consequences, as well as the emotions, hardships, and the lessons they got from the whole experience.
And it built up the characters as well.
Also Tatsujin, it can get sad, but there are also some fillers after 13 or 14, some of them are *really* nice. It goes back into srs biznis at around 19 or 20. but, those "non-srs biznis" eps were imo, really nicely played.