Director Lenny Abrahamson seems to be mocking art, but is doing so with love. And part of it is actually a true story: Frank, the character, is based off the comic persona of the late Chris Sievey, a comedian and musician who wore a fake head in one of his acts. In the film, Frank is not a comedian but a mentally ill musician revered by those around him. He almost never takes the head off, which means Michael Fassbender must rely solely on his body language to play the part.
Overall, the above trailer doesn't give away much, but it seems to be toying with a few questions: What's the difference between insanity and genius? Can people tell the difference? Does it matter? And, what do you do with your papier–mâché head when you shower? (Variety)