> If your iOS app uses custom controls and deviates from the Apple design language, your design is rightly criticized.

Not necessarily true, even ignoring games (which are a whole 'nother bucket of filth) deviating from Apple's guideline and creating your own aesthetics can work nicely.

It is a huge amount of design and implementation work, especially if you want to match the spit and polish of the built-in solutions, but because iOS applications are "full screen" it can in fact work better than on a desktop: there's no chrome with different aesthetics around.

Tapbots has been pretty successful at building up and using their own non-native aesthetics. They're completely insane though, their attention to detail is even higher than the platform's.