More than any other reason, the user experience (UX) of the Kindle Fire HDX convinced me to buy it. Amazon's Fire OS used on the Kindle is not only designed to be easy to use, it is very efficient.
Android purists will argue that a full Android UI is superior to Fire OS, but I've come to disagree with that view. The Kindle home screen is a gem of a design, as it puts the things you use most where they are most easily accessed. This is accomplished in three areas of the home screen: the carousel, apps at the bottom, and the thin strip of content at the very top of the display.
The carousel is what makes Fire OS such a joy to use. Every time you open an app or some content, the icon for it automatically appends on the left of the carousel. It's common in normal use to see apps, ebooks, music album art, and preview thumbnails of documents side-by-side in the carousel. This makes is simple to return to something you were doing earlier.
I have lots of apps installed, but I suppose like many users I tend to use five or six of them most of the time. Given the way the carousel works, my main apps are right there on the screen a tap away. The carousel content changes dynamically, and that makes it subtly powerful. It's like the Kindle always puts what you need right where it can do the most good. That's the mark of a great user interface (UI).
The app 'dock' at the bottom of the home screen isn't really a dock, it's a dynamic area where you pin the apps you want on the home screen. There can be as many or as few as you want, as all apps live in the Apps segment that's on the top of the screen.
This custom home screen area always displays one or two rows of icons in landscape or portrait, respectively. You can pin any apps you want and put them in any order you prefer. This turns the bottom of the home screen into a dock of sorts. It's a convenient place to put your most frequently used apps for easy access, for those rare times when one is not right there on the carousel.
The thin strip of content categories along the top of the screen provide easy access to apps and content on both the Kindle and in the Amazon cloud. The Music category not only taps into your music library, both local and online, it also accesses the Amazon Cloud Player integrated right in the OS. There is no separate app to deal with to listen to music, just tap on an album on the music page (or on the carousel), and the music plays.
Kindle book content works the same way, and it's no surprise the HDX is a fantastic ebook reader. This is the best version of the Kindle app on any platform, which is how it should be for Amazon's tablet.
Fire OS is optimized for the good hardware used in the Kindle Fire HDX, and it's the smoothest Android tablet I've ever used. The interface and apps flow fluidly on the screen. There are no lags, nor herky-jerky scrolling. The HDX is pure joy to use.
Next: Sideloading apps; Value proposition; Is it better than the iPad Air?