I have a Fire Phone. I couldn't resist, when they were $199 and include a year of Prime (which I already pay for), it's $100 for a quite high end piece of hardware. And, the hardware actually is really great. Camera is great, display is great, touchscreen is great. 2GB of RAM and 32 GB of storage. It's very high end phone hardware at a very low end phone price.
That said, it's an awful phone. The OS feels clunky and old. The 3D stuff is, as mentioned in the article, gimmicky and pointless. Firefly is just annoying (it seemingly pops up at random, as if to say, "Hey, wanna buy something? You should totally buy something."). The interface, where it has diverged from Android, is confusing as hell. Menus pop up when you rock the phone, or shake it, or something, I dunno. It just randomly pops stuff up sometimes and I don't know why or how to replicate it. The status bar is disabled by default and the launch screen is more limited and frustrating than the original launch screen on the G1 (the first Android devices). Camera comes up every time I try to adjust the volume because the buttons are right next to each other. This also seems to be a trigger for Firefly...maybe. I honestly don't know how Firefly is called into existence, but it's popped up dozens of times since I've owned the phone, none of which were times I wanted it.
Amazon built the phone Amazon wanted. It's not a phone designed around customer needs/wants, at all. They even pulled out a bunch of functionality for seemingly no reason other than they want people to buy more things from Amazon. For example, you can't use your music on the device as a ring tone or alarm (a feature that has existed in Android approximately forever). But, Amazon will sell you ring tones.
It is possible to sideload the Google Play Store, which is one redeeming characteristic of the phone...so, I have GMail, Firefox browser (which is not in the Amazon store, but can also be sideloaded), calendar, docs, etc. But, it's still not a pleasant phone experience. The UI is needlessly opaque, and the unique features of the phone are pointless or annoying. The unique features are also not at all discoverable. I didn't know Firefly could recognize music and art, that's kinda neat. I don't know how to use any of the buttons and movements to make the phone do things. They seem nearly random when I try to use those features, which is quite frustrating.
I gave it, I think a 3 star review, at Amazon, on the strength of the hardware, the very low price, and the fact that Google Play Store can be sideloaded relatively easily. But, I would never recommend it for someone who isn't a tinkerer. It's just too confusing, and the native apps (for email, maps, etc.) are weak.
Edit: And perhaps the most frustrating thing is that there is no back button. You have to do a swipe gesture from the bottom (the very bottom, or it scrolls instead) of the display. I sometimes find myself having to attempt this a half dozen times to make it work. It is incredibly frustrating; and worse, I find myself doing it on my Nexus 7 (which has a back button and doesn't respond to this gesture). It's training me to be their kinda stupid.