Took a bunch of photos today and gotta say I'm not impressed by the camera. Felt that at least when using the camera button it had a delay before actually taking the photo and often seemed to focus on something close to the camera (like a chainlink fence). Using the digital zoom really gave rather artifact filled and too soft pictures. It sometimes takes a long time to start the camera program (like over 5 seconds during which it looks like the OS is doing nothing) I really hope that Sony fixes these problems when they update their camera software. As it is, not that impressed.
My phone's screen white balance was also a bit off but thankfully Sony provides a settings options where you can adjust that though it works a bit backward (instead of substracting the offending color you add a bit of the ones that are not the problem, e.g if it's too red you add green and blue). Not by much but just a little. I wish this setting was stock in every Android phone so people would not have to deal with tint issues.
It might be that the warmth of the phone is entirely normal operation based on what other owners have mentioned. It's just that I'm used to the Galaxy S4 (i9505, running Google Play Edition ROM) and it only gets warm or hot when you download lots of apps or play a game etc. The Z5C gets a bit warm (back around the Sony logo and on the front touchscreen) when it's used for 20 minutes or more doing anything really. I checked temps with CPU Temp and the Z5C was running up to 10°C hotter than the S4 on the CPU at times and battery seems to go to 40°C quickly whereas S4's battery stayed at 30°C.
I don't find this at all impressive because I don't experience any real increase in speed, in fact in a few apps (Tapatalk and Bacon Reader, neither of which is great software to be honest) the S4 is smoother. In benchmarks Z5C gives much better results (for example Antutu score is ~55000 on Z5C and ~30000 on S4) but this just doesn't translate into real world performance at least for what I use my phone for (web browsing, Facebook, messaging, photos, navigation).
I really do want to like the phone but just don't feel like I'm getting the upgrade from the S4 I was hoping for. It's not really much more comfortable to use one handed (due to the more angular shape at the same thickness), it doesn't seem to perform any better and has a smaller, lower res screen. The main improvements are better battery life and the fingerprint reader (which is fantastic and in perfect position). I also really like the smaller LED notification light, it looks more elegant.
If the phone didn't get noticeably warm in basic use and had a bit more screen (and thus less bezel), a contoured back, 1080p resolution and better camera software it would be my ideal smartphone. Sony's Android implementation is near-bloatless and very close to stock.
TL;DR my old S4 is surprisingly good.