Responsive, efficient UI that somehow remains uncluttered despite the surprising depth of functionality.
No companion Mac app.
Darkroom has been the go-to photo editing app on my iPhone, so I'm very happy that the same simple-yet-powerful functionality is now available on my iPad, too.
It's clear that an obsessive amount of thought has gone into refining common workflows in Darkroom. Rarely do adjustments take more than one or two taps or swipes, which for me makes using Darkroom feel a lot more efficient than Lightroom's many dropdown menus and modes.