Having played around a bit, visually it's a huge improvement, although maybe a bit excessive on the "animation" of the various menus opening on the left.
Overall it looks and feels a lot more professional than earlier versions, it's really quite amazing what a UI/UX overhaul can do.
At the same time, it's not a UI that's just there to look fancy, like what QNAP, Synology, etc. largely does.
There's also a new notification area where errors etc. can easily be copied from, which is great for fault finding.
Overall it feels a lot slicker and informative, even though there clearly is work to do, as for example performance graphs are all a bit weird now, as they scale poorly in the new UI.