My thoughts so far on 4.2 (running on Nexus 7):
(I’ll update this as I run into more features/thoughts)
I don’t like that my icons are smaller on the bottom/main menu row.
Some of my favorite apps are not working with 4.2 which I trust will resolve soon but I’ve not run into this problem with a system update before.
I love that I can swipe out gmail messages to archive them.
I really like lockscreen widgets, although I don’t think they’ve cleaned up/maximized layout yet. My guess is that it would look perfect already on the Galaxy Nexus phone.. (but Verizon’s not likely to release 4.2 until perhaps Summer or Autumn 2013.)
The new clock/stopwatch/timer is an excellent feature to make standard and works cleanly.
Having a built-in “gesture” keyboard is great, but Swype is WAYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY better.
Daydream (/screensaver) is so fun!! Will be even better when they allow a bit more customization, such as on Photo Table feature: # of pictures allowed on screen and how frequently to refresh and whether or not to pull in random or in order, etc.
Okay I’ve played around some with the multiple users feature now.. it’s solid, though I expect in future they’ll have to offer ability to deliberately share/send text/files/etc. between the accounts. Here’s a good tour of the features.