I've been running this build since Friday and found a couple of problems:
1) after waking up from sleep, WiFi doesn't always work. The WiFi icon stays white instead of blue and I have no data connection until I turn WiFi off and back on (or leave it off and use 4g/3g)
2) can't find battery mode selection (GB had "performance" and "battery saving" and "night mode" - this could be the problem with #1 but I can't find the menu to change it - maybe it hasn't been added yet.
3) UI is a little inconsistent across the OS. In some places you get icons in the "menu" pop-up, in some you get text...like some places you see a trash icon, other places you see the word "delete"
still, very usable.