[Xperia Z5 Compact General] smilemantts:
Overall I've been a pretty happy Z3C user. My two main beefs with the Z3C we're some build quality issues (screen on two devices would pop/flex) and I've never been crazy about the photos. They were just ok.

So here's my take on the Z5C:

First, the fingerprint sensor changes a lot in terms of how I interact with the device and how quickly I can access the device. I really like it. However, as reported elsewhere the scanner is not always completely reliable if my finger has recently been wet, cold, etc. I'm still exploring how to optimize my fingerprint readings, and it may also be a case that my fingerprints are a bit worn down and so fingerprint scanners in general may not work very well for me (this is the first one I've tried using). But overall it's an excellent addition and I love the location of it on the side.

Second, the speed of the 810 processor is phenomenal and makes the phone feel so much quicker. This is something I did not anticipate liking as much as I do, and it has been a real pleasant surprise. If you're a Z3C owner and on the fence about upgrading definitely do not use the Z5C unless you're ready to move up to it as I think you'd have a hard time going back to the relatively slower Z3C.

Third, the build quality has dramatically improved on the Z5C. It feels much more solid and sturdy; a firmer hold in the hand. Z3C was much more slippery, bigger risk to drop. In addition to the screen pop issues I had, my Z3Cs always had more flex and creaking than I liked. Really glad Sony did away with the second flap/compartment on the Z5C, which I'm sure helped reduce device flex. The new SD card/SIM compartment closure feels more solid. Making the USB waterproof was also a great move. I thought I might miss magnetic charging, but I'm not.

Fourth, the audio quality, in terms of both phone call quality and speaker music, is much improved. I can hear people much more clearly on this device than the Z3C. I also play music from the speakers when I jog, and the sound quality is much crisper. I want to also say that using my headphones (aptX Sennheiser Momentum wireless) that sound quality is also slightly improved, perhaps due to a better DAC? I'm not 100% sure about this and was already pretty happy with the Z3C headphone performance.

Fifth, battery life seems to be about the same, which is a relief. I had heard some people were experiencing worse performance, but I have no problems getting through the day with 30 to 40% still left after heavy use.

Sixth, the display seems to be improved. Slightly sharper and more vibrant. I didn't expect this and I'm not quite sure why this is the case because the resolution/spec has not changed much.

Seventh, the location of the volume button has not been a problem. Some early reviews complained about this, particularly on the bigger model, but I find its placement on the Z5C just fine.

Eight, I'm not a gamer or 4K video shooter, but I have not experienced the phone overheating or getting too hot, which was something that was a concern.

Ninth, I have not experienced any of the software stuttering that the Verge and others have reported. I'm wondering if some of the complaints here were on an earlier firmware.

Tenth, using the screen in the tub when the screen is wet, or with a wet finger, also works a lot better. I think Sony rolled out this improvement in the Z4/Z3+. Much appreciated.

I have not had a chance to thoroughly test the camera yet or do a side-by-side with the Z3C, but so far (especially after the 2.0 upgrade) I'm happier with the Z5Ccamera.

So overall, well done Sony!