Just upgraded my nexus to 4.2.
Lockscreen widgets look like they'll be pretty handy. Right now there's only messaging, gmail, and calendar. Photosphere seems pretty cool too, although it would be nicer taking one on top of a mountain instead of in my apartment.
They took out the slide left/up for camera/google now and made it so sliding the lock anywhere unlocks. Swipe left for widgets, swipe right for camera. Not sure how I feel about this. Odd that the pull down toggles for wifi, etc aren't actually toggles but shortcuts to settings. Seems to ruins the point.
All the small improvements are nice. Google seems to be getting rid of a lot of the inconsistencies - Pinch to zoom in Gmail, group messaging with iphones apparently works now, clock vastly improved, etc.
Haven't got a chance to try the stock gesture typing much but when I did it worked well. I'll have to try it for awhile and see if I end up going back to SwiftKey. I read that it's a more noticeable difference on tablets...so maybe when I get my Nexus 7...