This phone is a joy to use because:
Simplistic yet beautiful and ergonomic design.
Excellent on screen keyboard.
Fresh but extremely intuitive interface which is very easy to learn and addictive so much so that the other leading os would seem outdated and non user friendly.
Excellent HUB concept which is best in class for communication and social networking getting all emails at one places.
Excellent interface which is a boon for multitasking fanatics and the interface is built in such a way that it very easy to regularly terminate apps which are not being used and hence makes the device run smoother.
Excellent computing hardware which is in blend with the QNX based OS making the device run without any lag (a bane in earlier OS) without boasting top of the line hardware specs. I have installed almost 52+ external apps and in the past couple of months w/o loosing any time fretting over os hang issues.
Excellent android runtime which makes the app difference vanish to a large extent. etc.find it yourself
Things which I want to improve:
Camera quality needs to improve may be something in the camera app since the camera works better when used thru Instagram.
Support for google play which will make more android apps to run smoothly.
Equalizers in music player app.
All in all excellent phone with great build (better than iPhone 5c) superb os and excellent interface makes this extremely value for money.