Having used Lollipop on G Pro 2 for a few days now, I still find the battery life to be significantly worse than when I was on Kit Kat. Perhaps my battery is now older, but I find that on idle overnight the battery level dropped by around 15%. A 100% battery now will probably last me about half a day, as compared to easily a full day when I was on Kit Kat.
Another upgrade I don't quite like about Lollipop is its sound profiles. In the Do Not Disturb mode, there is a further differentiation between Do Not Disturb - Silent and Do Not Disturb - Priority, if you forget to choose Priority, alarms in (Do Not Disturb - Silent) go off without sound or vibration. Personally I find this to be less intuitive than compared to Kit Kat.
If you can live with the poorer battery life, the OS upgrade itself is indeed better.