My experience...
I'm with Bell. Everything went good for me during the update. Phone went really hot during installation but came back to normal after. Some Google Play services crash but after restart, everything went smooth.
I notice that my battery is a bit more hungry now with Lollipop with screen on. Inverse on standby. While sleeping, my phone was loosing 10% overnight with KK and now about 5%. I did a factory reset couple days ago and I see absolutely no difference than before so I'm not convince that this is a necessity.
I'm experiencing some problems with my bluetooth connection in my car also. It was working perfectly before, but now, my music stutter at some random time. Never experienced that with KitKat. (But I was with my iPhone since iOS8 lol!)
Clearing cache, factory reset, reboot, pair/unpair didn't fix my issue.
Beside that, I love some of the new Lollipop features, like Smart lock and lock screen notifications.
I also prefer the orange color for the messaging app

(There's an entire thread on this

)