Comey sent out a letter that referenced new found e-mails that could be important to the ongoing investigation of Clinton's e-mail server. The vagueness of it basically left a lot of questions, which also lead to a lot of misreporting, particularly about the case being "re-opened" despite the fact the case isn't technically closed. The lack of real information lead to a big freak about, because assumptions were being made that this was some kind of major development in the e-mail 'scandal.'
As it turns out, the e-mails found were on devices belonging to Anthony Weiner, that was part of a separate investigation, and it's not even clear if the e-mails on these devices are even new. No one has any idea if these even have anything to do with the Clinton case, it seems, and there's more and more questions about why Comey sent the letter, why he was so vague, and basically questioning if the whole thing wasn't just a partisan-driven move to try and dumb down the momentum Clinton had. There's been a lot of argument for and against Comey here, but the more and more we learn, the more politically driven it seems, and that's why a lot of the talk is divided right now between more e-mail speculation and Comey's questionable actions.