Running 2.2 for about 24 hours here. I played it safe and installed to a spare SSD on a second machine, swapped drives and restored the 2.1.5 configuration backup. Only running a few packages, snort, nut, avahi and they reinstalled fine after the restore reboot.
The only minor thing I've noticed is that the gateway dashboard widget is showing impossibly low RTT values, on average about 5ms when it should really be about 25ms, which is what 2.1.5 was showing (ping shows about the same, mid 20's).
Thanks to those involved in this release!