The Kindle Fire HDX is firmly entrenched in the Amazon ecosystem, and that means there is no access to the Google Play Store. Apps must be purchased from the Amazon App Store, which has a much smaller selection than Google's. That said, I have yet to find an app I want that is not available in the Amazon store.
Amazon realizes that its app selection is not the best, so it has enabled the Kindle to accept sideloaded apps. These are apps you can find on the web and copy to the tablet over the micro-USB connection. This process is simple, and once the app is on the Kindle you install it. These work fine and greatly broaden the usefulness of the Kindle.
You can also install Google Apps through a process detailed on the web. I have Gmail, YouTube, Google Play Music, and Google Search installed on my Kindle through this method. It's straightforward and works well. You can actually install the Google Play store app, but it requires some serious hacking. I don't find I need it with the simpler method of sideloading apps.
The value proposition
My Kindle Fire HDX 8.9 is configured the same as my iPad Air. They both have 64GB of storage, and LTE. I gave $829 for the iPad Air, a princely sum. That makes the Kindle a bargain at $579. That's a big difference in price, and factored into my decision to buy the HDX.
The Kindle Fire HDX has hardware just as good as that found in tablets costing much more. Some will argue that it's not real Android, but as detailed in this article I find it to be better than Google's version. Amazon has nailed it with the Kindle Fire HDX and Fire OS.
Kindle Fire HDX owners should not overlook the Origami Case from Amazon. This case is one of the best I've used on any platform, and is incredibly useful. See it in action on my review of the Kindle.
Is it better than the iPad Air?
No. It's different than the iPad, and some will like it better, others will like the iPad better. There are some things I like on the Kindle Fire HDX more than similar things on the iPad, and vice versa.
The Kindle Fire HDX has enterprise features built into the Fire OS. It has VPN capability, a full Office document viewer, and wireless printing, making it a good BYOD solution. Amazon also has WhisperCast, which allows the IT department to remotely support Kindles used in the workplace. This includes the ability to push corporate content to the work force using Kindles.
I don't recommend products over others as everyone has different things they like better than others. I like using my iPad Air. I enjoy using the Kindle Fire HDX.