Just updated my 4xl last night to A12. OK I like the big, funky clock on the lock screen but that's about all; couldn't they have made the date, temp, and battery % a bit bigger while they were at it? Lots of downgrades from A11 IMO.
On 11, I was able to tap the "at a glance" widget's date to launch the calendar app. Gone on 12.
Putting the phone into vibrate on 11 put a little vibrate icon up into the top status bar. Gone on 12.
The "wallpaper and style" section of 11 was so much better. You could do different shapes for app icons. Just round ones on 12. And since the themed icons on 12 only works with Google apps, if you have any non G apps on your homescreen (and don't most of us?) the uniform theme is broken and looks bad.
And, as others have stated already, I really don't like seeing only 4 quick toggles when pulling down from the home screen (down from 6 on A11).
Pretty disappointed.