1. I have noticed many complaints that the volume on the front facing speakers is just too low.
Well I've noticed the same issue since the Z2, the Z3, Z3+ and now this, that the bottom speaker, if you cover the top, hardly produces sound!
I hope Sony finally fixes this problem.after so many years of this issue now!
2. Display contrast enhancement and no chance to fully use 4K.
After measurements it is clear that the Z5, especially the Z5 premium could be a lot brighter from its display, if the contrast enhancement would be calibrated correctly. Due to rough calibration, the display loses over 100 nits and more, just because of none perfected calibration. For a top of the line device, calling itself premium, this is a no go!
Also, there is no chance in actually selecting the display to operate in 4K.
People are being forced to render and see everything in 1080p.
This is no premium offer for a smartphone with an attached name such as "PREMIUM"!
For a premium device, you should expect premium offers, such as more software tweaks, a special experience, convincing you that THIS IS a premium device.
3. Camera post processing.
Most of the time, in PERFECT LIGHT CONDITIONS, the camera works really well.
But how often do you have perfect conditions!?
As soon as you have low light conditions, or light coming from an angle, or even in "normal environment" conditions, post processing really messes up the pics taken, taking away an awful a lot of detail from the picture.
If you compare pictures to almost all competitors, you'll find that sony's post processing really kills a fabulous picture, which is a shame really, because Sony really does have an excellent sensor and a real nice lens with the best processing hardware.
So far, all aspects referring to the Z5 line show that there is still a lot to be done concerning software.
The premium should especially be looked at, there is much space for improvements, especially for a premium line and considering the price, until now, it's only a standard Z5 with an overblown display that doesn't even render in 4K 7needs you have a 4K movie and watch it on sony's video app.
Upscaling hardly counts, there should be an option for consumers to choose whether they would like to have everything displayed in 1080p, QHD OR 4K.
Overall, it's not a bad line but the premium is missing everything making it worth its name.
This is just an opinion of over a certain amount of users asked and own experiences on the Z5 line.