That episode 4 certainly felt like it should have been three episodes, with proper introductions, explanations, and stuff. Maybe I remember random names a bit more than some among the anime only audience might due to reading the Accelerator and Railgun manga, but even so the episode felt like like a recap of things I'd never seen. Maybe I should have read the Index manga, not the two others, but I hate Index herself so much I never wanted to. That being said, I don't know how far the Index manga even is. I doubt I'd bother to read the novels.