I'm only speaking on the negatives here.
There are two scroll bars on the right hand side. The menu scroll bar and the browser scroll bar (expanding on what one of the comment above says). This is a poor design, and not sustainable. May be you guys don't see it on your mobile, but it looks really bad on the desktop.
I have also left couple of comments on the news article about this new calypso editor. The sort order of the category list is alphabetical, which is unlike how it is in the Classic editor. The large sized featured image at the top of the screen is useless. The new editor also processes the short code, display-post code, and html table codes in the Visual tab. It then adds and clutters the codes with additional html codes in the html window, cluttering the whole space. This is totally not usable.
It seems obvious that your designers are either not regularly blogging themselves, or they are designing this thing for mobile phones?
In general, the amount of time and energy WordPress has spent in redoing the TinyMCE editor over the years, is so unfair to the whole platform development. You started redoing the editor several years ago and you have still not managed to get it right. There has been lots of complaints and lack of adoption. The debate between the mobile and desktop world; the beep beep bop; the right versus left menu....The classic editor still stands as the one most people want to use.
Thank you for keeping the classic editor as is.