Frank is what I call a "hail mary" piece. Somebody got a picture in their head. A powerful moment. One full of potential and energy bordering on magic. And they made a film just to end on that moment. And it either works, you make it work, or it falls apart. They make it work.
Frank starts out being about one guy, then it's all about a different guy. Which is slick. Because part of your attention is diverted. Which sets you up to really be blindsided at the end. And it's all done with emotions rather than a stark manipulation. You are lent a mild detachment on purpose because of a series of events and how they make you feel, to put you in the right frame of mind to have large contrast and magnitude bias when you are hit with the final scene. It's brilliant.
But it's all about making it there. They pepper the trip to the end with alternating turns of humor, discovery, and character building. It's an effective combination. You'll see this technique employed by Anime. Everybody is top notch. Maggie G really shines. And Michael Fassbender is incredibly good. Like award winning good. He could win an award just for the last scene.
See this film. See it knowing the reward is at the end. And the reward is fantastic.