There are essentially three types of Apple TV 4 apps. The first, such as Netflix, are written hand in hand with Apple, and they're designed to show off the platform to its fullest. Americans get several of these full fat apps, but we just get Netflix, iTunes and Apple Music. They all support Siri Universal Voice Search, Top Shelf, Visual Scrubbing, and user interfaces which either use the white iOS 9 style white templates with lots of art and transparencies, or are written with fully custom user interfaces in true iOS code. Netflix is a 100% all dials on max Apple TV app. It sets the standard by which all other apps can be judged.
The second type are Apple TV 4 apps written without Apple's help. They can do everything the first category can but they can't access Siri. Not yet anyway, but next year Apple will open up Siri to all apps. A good example of a really high end Apple TV 4 third party app would be MUBI.
The last category are the ports. These are old Apple TV 2 or 3 "apps", but they're little more than pages of text on a black screen. They have none of the new Apple TV features or user interface. YouTube is a good example of a lazy port, and Now TV is another.
The last category shouldn't exist, but laziness and corner cutting is surprisingly rife at big media companies. Sky may redo Now TV for the Apple TV someday, or they may not. I'm not holding my breath. I dare say Sky could have taken route one, and worked with Apple to create a state of the art platform selling Now TV app with all the trimmings including Siri. It's too bad for everyone that they didn't.
