PAGES ON THE LEFT
Previous versions of Acrobat had the ability to view page thumbnails on the left, and at the same time view and reply to comments on the right. The new version closes pages when opening comments, and closes comments when opening pages. Being able to quickly go from page to page to review comments is essential, and this disconnect from visual to text is extremely counterproductive.
I came here to say this - switching the pages pane to the other side is the most unintuitive and annoying design decision I've ever seen in an Adobe product.