I've only heard bad things about it - https://www.youtube.com/watch?v=BpsMkLaEiOY
This phone isn't going to kill the iPhone - in fact it would take a big screwup on the part of Apple for people to start migrating away from its products. Not that Apple is incapable of screwing up, but so far they've sailed their ship pretty well.
Apart from the hardware, there's the whole ecosystem of app developers, programming environments, cloud services.. Ultimately it's about who can attract the more talented developers - and that is a lot more difficult than snapping a faster CPU or better camera in your phone.