OP3 has a really good camera. Not Samsung/iPhone/LG/HTC quality, but not that far off either. I was pleasantly surprised by OP3 camera capability.
Battery was also a nice surprise, since I wasn't expecting much, but on just LTE I've managed to get 4:30. And the phone is ridiculously fast, probably fastest Android I have ever used.
As far as upgrades go, I wouldn't believe OP team much, since they tend to lie a lot! And faster the update comes, more bugs will show up. I'm speaking from fast experience here.
But on the other hand, I bet this phone is on par with Nexus when it comes to custom rom support, especially since OP is releasing almost everything open source, so I wouldn't worry that much about upgrades. OP3 is built for custom roms, so if you plan to get it, use that option. Better then sticking with stock