Re: OS Updates
As others have said, not too bad.
Sony are never first to new versions, but their commitment isn't to be doubted.
My Z1 came with Android 4.3, got updated to 4.4, and then updated to 5.0.
My Z3+ came with 5.0, and got updates to 6.0 and 7.0.
I'm on a Xperia Z5 Premium right now, and it came with 6.0 and has had updates to 7.0 and 7.1. I will be very surprised if it doesn't get an update to 8.0 at some point, but my contract's due for renewal soon so I may not see it personally.
When I say "Sony aren't first", I'd guess there's usually a lag of a few months or so from release of new version to Sony pushing it out.
Some security updates have also arrived, but my phone is currently on the 1st June 2017 security patch level - it would be nice if they were actually monthly, but they seem to be quarterly at the moment.
Overall I'm not unhappy with the commitment Sony have shown over the three phones I've had. I'm inclined to buy a Sony again, if possible.
My only other candidate was a Google Pixel - which will naturally have much better updates. But the next version is rumoured to have no headphone jack, and if that's true it can get stuffed. At the moment Sony have the best balance of great hardware, decent (light) Android customisation and a history of shipping updates. There's room for improvement, but compared to much of the competition they're doing pretty well.
Too long? Didn't read? You can expect two full OS version updates on a Sony phone, maybe three.