In the Sept 15 release, a new reply sidebar was added that replaced the unfolding of replies below a topic.  Thumbs down from me.  The flyout takes you out of the flow of the thread and suddenly you have to keep your mind in two places - the flyout and the original discussion area.  Yesterday, when clicking the "# replies" link, and the hidden replies simply unfolded at the location of your click, I was happy.  That made sense in terms of countering the scroll of death.  Today, when that same click causes the page layout to change so dramatically, I'm not.  Sub-replies are now displayed as a separate "page" within the flyout and you have to find and click the "<-- Back" link.  Sure, I figured it out, but it's not better than what we had yesterday.  It reminds me of Slack, and I don't like their approach either.