I like the new UI, it feels simpler and less gaudy. The drop down menu expansion thing is fine. I also prefer the redesign of the settings app. I find casting my screen and bluetooth works better. Windows has been missing something decent window snapping features forever and although it's a bit clunky I appreciate that it's there.
The only thing that has annoys me is the taskbar not disappearing when its supposed to, leading to it covering the bottom of maximized applications. Most of the time its not there but sometimes it'll just stick after coming up.
I didn't know about the android apps feature but I might give it a shot when I go home. Widgets I just haven't used at all despite being aware of them.
I still have win10 on my desktop. I don't remember the switch being painful when I went to the rolling release windows insider on my laptop. Frankly win10 is fine too, so unless there's an android app I want to play around with I wouldn't bother switching.