I came from a Sony Xperia Z1, and couldn't be happier with the HTC One M8.
- The build quality is outstanding, much nicer to hold in your hands and prettier.
- The screen is very, very good. The one in the Z1 was mediocre, viewing angles were terrible so when I turned on the M8 i couldn't hold my first "wow". Better color, better angles, outstanding.
- Speakers BLOW AWAY the Z1, there is no possible comparison, the sound in the HTC is unbelievable. I showed it to my girlfriend and she said the second "wow" (she owns a Z1).
- Super snappy performance, completely smooth transitions, minimize, restore and multitask. Sense 6 is a fine piece of software. Highlights works fine but I still find Flipboard better.
- The camera, despite the hardware of the Z1 being better, gets better results than the Z1. The Sony phone has extremely terrible software that makes the pictures grainy and blurry, when the HTC One makes pictures quite sharp and noise-free (love the focus speed).
- Battery life is a bit shorter than the Z1, but 3000mah vs 2600mah had to show somewhere. Anyway, more than a day and a half in one charge for the One M8 is a very good performance.
- The sound while listening to music on my 150? Sennheiser headphones is SO MUCH BETTER than with the Sony.
- Tap to wake is very useful, I rarely use the power button anymore.
Software feels much more solid, build quality is impressive, good camera, incredibly gorgeous screen and sound.
I love this phone