The Fire phone is a gorgeous hardware success in my opinion -- if you try it, it's fast and sleek. The Firefly scanner is super-convenient for shopping.
The show-stopper issue for me is the UI. It feels as if screen elements are sloshing, or hard to find, and the UI is hard to use when I'm in motion.
I expect the UI will be easy for Amazon to solve. The phone is a version 1 and a strong debut -- even if it didn't sell well.