Thor for iPad is a great case study, but I'd say it's actually a fine example of how the entire "flat versus skeuomorphic" debate has ultimately been misguided:

Thor for iPad is a great case study, but I'd say it's actually a fine example of how the entire "flat versus skeuomorphic" debate has ultimately been misguided: The app utilizes a broad spectrum of digital UI affordance to great effect, from literal object metaphor ("this is a synth; it has knobs that do exactly what synth knobs do") to abstract color and shape cues ("these controls aren't part of the synth but have auxiliary control over it and your project"). This layering of design language creates a useful divide between areas of functionality that can't be achieved when you're limited to "flat or skeuomorphic" as a binary choice.