Updated to 420 over the weekend. Its great.
As expected, outlook back button is not working. But other than that the "accompli" - renamed outlook - app is great.
Battery problem is also there. Not sure the about the cause - but wifi and second sim seems to be the culprit. I have both sims enabled and 1st sim is the data sim. its like this - when i go to office in the morning, battery is > 95%. and in the evening, by 8-8.30pm, its around 60%. But by 9-9.30 it comes down to 30-35% and when I plug it in, even then it comes down. I have to switch off second sim/some times data connection, sometimes wifi, only then it starts gaining charge. Anyone facing similar issue? its ok, i can live with it. I'll wait till red stone release. while plugged in, if it restarts after draining the battery, then the charge is shown as more than 50%. Its confusing.
About the update - the update from 8.1 to WP10-build 218 was not that smooth. but from 218 to 420 was smooth. The only issue i faced was that i did not get all the SMSes back. I had the sms back up on in 8.1 and the last back up was on Jun18th or so. I have set the SMS for a year to sync now, but many SMSes are are missing. many of them are IRCTC ticket sms, now I have to get them again 3 days before the journey date.
Oh! I miss the tasks view in 8.1 calendar but I have installed wunderlist - i assume MS wants all of us to do that, thats why they removed the task view from calendar in WP10.