I flashed the factory image the day it was available and I've been happy with it ever since. My battery life is longer, many of the notification quirks that I disliked were fixed, and the performance is no different than Lollipop as far as I can tell. I only experienced an incompatibility with one application that I seldom use and it has been fixed.
Every time a new upgrade comes along there are a slew of negative comments from people that haven't even attempted the upgrade. They blame problems with previous upgrades on Google while most of the time it was something that they have done. I flash a new factory image to my Nexus 7 instead of doing the OTA upgrade, and everything is fresh and clean. I leave my apps and data alone. I do the same with my phone and every upgrade has been great. Yes Google, like Apple and Microsoft, isn't perfect and some bugs creep into the release, but they have been minor compared to the benefits of the new release. They typically are fixed quickly too.