Installed .63 and did a hard reset from System > About on my Lumia 925. It's almost like I have a brand new phone. Definite improvements:
* Across the board: not only seems faster, but is faster
* Cortana is faster, behaves better
* Camera behaves better
* Paste from suggestion bar is almost always available.
* Mail's tile now shows the new mail count
* I have to manually terminate suspended apps much less often for operations in the current app to run
* Battery seems to last longer
The bad:
* PocketBible crashes on successful entry of username and password, and when trying to access the on-device library. I submitted a support ticket to Laridian.
* Wi-Fi seemed to get in a funky state where the quick-setting button would blink. Toggling Wi-Fi didn't resolve, but switching to a different SSID and back on the access point did.
Yet to try:
* Mobile hotspot: will it blend?
* If the still an issue that occasionally battery would mysteriously drain so fast that charging could barely keep up. Rebooting the phone generally stopped whatever unknown power-hungry thing was feasting away
* Installing on my wife's L640, currently running .29. Her impression of W10M so far is "this phone hates me." If WP7 was still a thing, that's what she would have been happy to stay on. Hopefully .63 will change that impression.