We had to get a new television for... reasons. Because it was black Friday, we were able to get a new television for less than $200. We decided to avoid getting a Roku, because we didn't want to pay the activation fee (and my Roku experience has always been terrible). So, Fire TV it was. Maybe it's just because I'm used to the luxury of an Apple TV, but Fire TV sucks!
The biggest issue is ads, and because of that, also privacy. There are ads everywhere. Integration with Amazon's Fire TV channels is baked into the operating system and are constantly pushed on you. And at the top of the home screen is a carousel showing you ads. You can't disable this.
Privacy is another huge concern. There are so many privacy settings that I had to disable. But the most baffling of them all, OCR. This feature fingerprints the content of external inputs to help improve your advertising. I cannot imagine a single person who would want to enable this (okay, I know a few). I understand they add ads to keep Amazon devices cheap, but do you really need all this?
Next, the interface itself is just horrible. I don't have much to say about this, it's a bad interface. You can pin a few apps to the home screen, but the rest are hidden behind a menu. And the app store has a sneaky trick where they automatically subscribe you to a streaming service when you download the app. You have to press a hidden button to just download the app without subscribing.
Finally, the entire experience is just slow. Sometimes the screen will just go black, or the OS will freeze. The whole thing feels janky. Amazon and good user experience don't go well.
If you want a good TV experience and you already have a TV, I would recommend just getting an Apple TV. They aren't too baked full of Apple services (yet), and aren't slow. If you have an iPhone and ethernet port and don't mind using your phone as a remote, you can find one on Facebook marketplace for like $10. These things just appear in people's houses like stink bugs in the winter.