Kinda annoying but with settings you can make the new reader usable. I keep the sidebar and pagebar as hidden as possible because I find it cluttering and ugly. Here's some problems I still have though.
1) I have to open the sidebar so I can click the manga title to reach a manga's main page, whereas on legacy I could simply go to the top of the page. The dropdown for chapter and group lists were always sitting at the top too. Could you just put that stuff back up there?
2) Similarly, I have to open the sidebar to reach the comments page, but legacy conveniently had that button on the top AND bottom.
3) To go to another chapter in long strip mode, I either have to reach the last page (which means waiting for each page to load) or, yet again, open the sidebar. I used to be able to change chapters with the left and right arrow keys at any time, or go to the next chapter by just clicking any page. It was very convenient.