The Amazon Appstore is a steaming puddle of absolute crap for the most part. I have a Fire tablet I play some simple games on, they're all chock-full of ads. Very few mainstream apps are available, though plenty of cheap knockoffs of those apps are. If you want something good, it's easiest to grab the .apk and sideload it. There are ways to install the Play Store but they're likely beyond most of the Fire's userbase. Regular Android users won't notice or miss this nor should they.

If I needed a tablet for anything serious, I'd buy an iPad or Pixel Tablet, both of which come with a real app store.