Been using it for about a week now and I can say this is a solid update. I have not encountered any critical bug but there is definitely room for more improvement. A few things that should be ironed out:
1. Delay on the lock screen if a PIN/pattern is used.
2. Occasional lag when launching an app.
3. Camera UI is still the KitKat ver and does not coincide with the rest of the UI.
4. No animation when bringing app the Recent Apps menu.
5. While charging, mA flow drops significantly when screen is on.