I ditched the Z3 for the LG G4, as I felt Sony was standing still whilst all around them seemed to be far more innovative.
It's interesting that many are criticising them for a 4K display, saying it's pointless in a hand held device, but Sony can't really win. I recall many doubters of 1080p before it became the norm, and and then the same for 2K. It's the nature of tech. that it's always being pushed further. They've also gone for the first side mounted fingerprint reader as well as losing the flaps for the IP rating (as they did in the far more incremental Z3+/Z4). Sure, I wouldn't mind a different design language, as Samsung have done, but then Samsung was notorious for being rubbish for that, so the only way was up. If they went for aluminium or plastic they'd be accused of copying HTC/LG.
If for one will be tempted by the Z5 premium if the actual performance lives up to the potential.