Recommend to Update: Yes.
Since, you're here reading these forums, you're more technically savvy, and won't mind spending the time upgrading and learning the ways of Lollipop. This will be useful when the less-savvy people in your life complain about all the changes; you'll be their hero. {I showed the changes to my wife, and she was not happy. She's of the "if it aint broke..." mindset. She may never get updated.

}
I installed the update using the PC Companion, and it went smoothly. Upon reboot of the phone, there was a small error as I had to update the "Google Play services" app, and there was an error about logging in with my account. After updating the app, the rest of the update went smoothly. The whole process took about 45 minutes.
I have an unlocked Z3 on T-Mobile, that I bought from Sony (US). I've heard that the T-Mobile-branded version has not been pushed out, yet.
Is it worth it? Yes, if you like to think that you have a new phone. My biggest concern isn't really a big concern. For me, it seems that the battery life has decreased a little. I'll be more definitive after a few days. I'm having more screen time, now, as I learn the ways of 5.0.2.
They've taken away the 'Close All' button from the Recent Apps. I never realized how annoying it is to close all the apps individually. I read that someone made a 'close all' button extension, but not sure where to find that off the top of my head. Also, the Sony "What's New" option, when sliding from the bottom, has been removed.
I still don't see where Group Chat has been added. Maybe, that will be resolved in 5.1. Can someone else comment on that?
For the good...(from what I can recall)
There are far more options on the lock screen, and far more notification actions that can be made. All these are to make you more efficient. I like the new dialer layout.
The O/S appears to be faster, but that could just be a trick as there are more animations between transitions to keep my attention. In any case, I like it. Google Chrome tabs have been moved to the Recent Apps, but they can be returned to their normal position in the settings.
There are more options for vibrate and silent modes as you can set a timer to bring back it back to ring mode. I like the Priority mode that allows only certain contacts to call/text loudly. However, this feature only works in vibrate mode. I would like it to work in silent mode, too. When, I'm sleeping, I'd rather only be woken by my wife and kids, and not have all the other vibration notifications, too.
That's all I have for now. Good luck. Have fun.