I did half a MLIS degree online. Ultimately, I quit because I live overseas (the reason for choosing an 100% online program) and the group work, which is bad enough anyway, was brutal with my weird time zone. Too many times getting up a 3 am to "meet" with my group.
Also, nearly every course had requirements to post to online discussion. As others have said, I found most of this to be a waste, particularly the "respond to a classmate". I did have teachers that noted that these responses needed to be substantive, not "I agree with Jane", and that helped slightly, but still felt somewhat pointless.
Also, I got the strong sense that some teachers barely even read projects. When I submitted a 10_ page paper, I'd wanted more than "48/50" as feedback. I know this takes time, but I feel like meaningful feedback to submissions, especially substantial ones, is owed.
Also, some teachers recorded video lectures, which often felt the same as in-class lectures. I though this was the best format, though that may be partly because of my learning style. And even better, I preferred the ones that had a little personality. It made me feel a bit more like it was a real person I was dealing with, and thus more comfortable contacting her with questions or concerns. I still remember that one woman's dog was sleeping in the background of her office, and she paused at the beginning to say something about "That's Fido in the background, joining us for today's lecture", or something along those lines. It was still a professional video, but this helped replace some of the sense of connection that is lost in an online format.