I got a notification from my phone about updating to Android 5.0.2 Lollipop this morning. I was already using it on my Nexus 4 and liked it, but it ran horribly slow on that phone. That was one of the things that prompted me to pickup the Sony Xperia Z3 Compact.
One thing that I was disappointed about with the update process is that it is not an OTA update. You have to do it through your computer. It's a fairly large download, so I guess I can understand the reasoning, but it's still disappointing after getting everything pushed to my previous Nexus phones.
The download didn't take too long on my 100mbps fiber but your experience may vary. After that the companion software doesn't seem to do much but drop the file onto the phone and turn it off for you. It then instructs you to turn it back on after unplugging and starts the install process. The actual install is pretty much the same as any other phone upgrading to lollipop, including the lengthy "Optimizing app" section.
So far I've enjoyed the update and haven't noticed any negatives to it. It runs circles around my Nexus 4 running 5.0.1. It's almost a completely stock Android experience with minimal Sony spread on top of it. The only thing I've really changed from Sony's default is the keyboard. I found that the stock Google keyboard is much better than the Xperia keyboard.