After having 4.2.1 for 24 hours I think it's pretty good for the first leak. I'll be keeping it
Things i have experienced:-
+ Dashboard works great apart from sms
Notification in status bar when I put in headphones and choice of apps that can be used with headphones in the pull down notification area (even with Nova).
Voice commands work great.
Battery time is about the same as MA1, around 17 hours with heavy use (not games)
- Had a problem with sms but fixed after I cleared data and cache.
Screenshots don't load in Google play.
Can't use any other fonts apart from those pre - installed.
Overall I think it's great! I had to reset data and clear cache 2 times to get the phone running smoother.
Flashed with Mobil Odin Pro full wipe twice, rooted with Ever root.
(my first post ever!)
Edit: Battery not so great today when I have Google Now activated.