Michael Fassbender did not receive an Oscar nomination for portraying the titular character of Frank.
Although Michael Fassbender plays the titular character the lead of the film is actually Jon (Domhnall Gleeson) the sane newcomer who by chance becomes a member of the very bizarre group of musicians. The leader of the band being a man who never takes off the papier-mâché head he wears. Michael Fassbender must give a performance a la Claude Rains in The Invisible Man in that it's a step above a vocal performance as they are allowed to physically portray the character as well even though they cannot use their face. In terms of his voice Fassbender's has a great voice for a character like this since there is something distinct and unusual about his voice. Fassbender's style of vocalization is rather interesting in that he does keep it a bit of a mystery whether Frank's weirdness is just something that's delightfully eccentric, or rather that he is a seriously disturbed individual.
Fassbender is certainly enjoyable in the role particularly when Frank states his facial expressions and brings a certain warmth as he at least states his interest in Jon's music with his "welcoming smile". Frank though is an enigma though as one can never even be sure of that support exactly since you don't know about his face. The best help comes from the physical expressions which Fassbender handles rather well. In the moments of comforting Jon Fassbender has a strong extroversion about Frank's movements. Again though the possible insanity though are in technically what Fassbender is more well known for is the extreme intensity where there seems to be some possible violent tensions within Frank. His most entertaining physical manner though is when he is performing as Fassbender plays these scenes as an over the top showman as every movement is a bit of a broad gesture.
Although Frank and his band seem to be getting off well enough, well aside from a few setbacks like a suicide, but things turn for a worse when Jon kinda takes over leading them to a concert where they may be very poorly received. Frank starts to break down and Fassbender is effective in portraying Frank's physical manner becoming far more introverted, as though he is hiding in himself all the more, and even the way he speaks becomes far more modest. The film does choose to give the mystery away about Frank, which is that he is merely mentally disturbed which in no way fueled his ability as a musician. It goes even so far to reveal Frank's face so we do finally see Fassbender in the film. His scenes without the face are brief, and Fassbender is fairly straight forward in simply depicting Frank as a deeply troubled man nothing more. Fassbender is affecting in his final scene where Frank finally reconnects with the Band showing that Frank simply never was what Jon saw him as. I must admit on re-watch I found Scoot McNairy's brief performance and Domhnall Gleeson's leading work more noteworthy. This is still fine work from Michael Fassbender, and an example of a good performance that barely makes use of the most expressive part of the human body.