Wow, 4.2 has some great stuff! In fact, AC is reporting that one person has ported the 4.2 camera and gallery to the Galaxy Nexus
I definitely look forward to photosphere and Miracast. These allow you to take full omni-directional pictures; and miracast allows you to use a big-screen HDTV to mirror what's on your Nexus screen (adapter likely required). Very handy indeed.
As far as other enhancements: Google Now gets smarter with upcoming movies, package tracking, flight schedules, restaurant and hotel reservations, etc. Oh yeah: Google's gonna beat out Swype at their own game, adding a swipable keyboard input with uncannily accurate predictive text and automatic spacing between words. Daydream uses news headlines or photos as a screensaver while docked or idle. And 4.2 for tablets ONLY allows multiple user accounts
While I'm not a swiping fan, I think the rest of it is a quantum step forward... and I so look for JBSourcery to be adding it all as it comes available in AOSP!