I'm an admin, so I guess I can't speak form direct teaching experience... From what I've heard from faculty at my institution, the redesign is more "clicky", and what they really want to come back in the redesign is a threaded discussion option where everything is displayed on a single page. There are numerous reasons for this, some having to do with grading, some with content, and probably other reasons too. I think the issue is really that different faculty and/or coruses have different needs. The redesign seemsto be focused on meeting needs for people who did not like the "original" discussions, but perhaps didn't account enough for people who were happy with the "original" discussions and just wanted some additional features added (like @ mentions) without a total UI redesign. I must say that I am glad I don't have to make these kinds of decisions, as I'm sure there are a lot of tough choices going into projects like this.
-Chris