My main complaint is that there isn’t a consistent experience between apps. Things are in different places, actions do different things in different apps, no gesture support, subpar players with horrible scrubbing, etc.
I think all apps should be held to a few basic UI/UX standards so going from one app to another isn’t a completely different experience.
The attached photo is just one example. Within the Apple TV app itself, long pressing an icon brings up this great menu allowing you to go straight to the show or the episode page. Long pressing in most other apps removes the show from your now playing list! All of these conflicting actions need to be rectified.
I think the "new" player UI (tvOS 15?) is very unintuitive. Very difficult to change subtitles and audio track. In the older UI you would just swipe down. It was clear and consistent.