I have only had the Xperia Z3 a day but I am ready to post some initial impressions

The display is beautiful. The colours are vibrant but not over-saturated, they appear to be reasonably accurate. the viewing angles are excellent. The 1080p resolution means the display is incredibly crisp - I do not miss Quad HD whatsoever.

I am really enjoying the quality of the audio, which seems to be slightly better than the Z2. The speakers may be a little bit quieter than the Z2 but the quality is improved: the bass is richer for example. The fact that the speakers are stereo is a massive advantage of this phone and is something that in my view, is a major selling points for phones nowadays.

The build is excellent. The sides are now rounded off, which means the phone is far more comfortable in the hand. The aluminium construction feels very high-quality and it has that "cold" feel in the morning which I like The back of the Z3 is a slab of glass (as is the front), which has the disadvantage of being very finger-print prone but it does feel quite nice under the fingers.

The button placement in my opinion, is really good. The power button is naturally where my thumb rests and the actual button itself is massively improved over the Z2: it feels much more "clicky" and tactile. The volume rocker is below that - unlike on the Z2, it isn't curved, it's completely flat. In my opinion, this isn't much of a loss, the volume rocker still feels very tactile and the volume up and down buttons are easy to press. Differentiating the buttons (e.g. when you're in a dark room) is very easy as they feel so different. Have a dedicated camera button is excellent. It allows quick access to the camera and allows focus by half-pressing it and then pushing it down the whole way takes a photo.

Those are my initial impressions. I'll keep this thread updated with anything interesting I find and my full review will be coming soon!

Any questions, let me know