I was interested in it because I thought it was about Frank Sidebottom (who was played by Chris Sievey), a Northern English comedian who wore a large papier mache head on stage, and whose jokes and routines were based around gentle northern humor. I missed out on all that, and Sievey sadly passed away before any of his slight fame could wash up over here in these great USAs of America.
It isn't based on Frank Sidebottom, I learned, when I started watching and the guy with the gaint round papier mache head had an American, as opposed to Cheshire, accent.
I rapidly looked it up and apparently it's based on an idea about Frank Sidebottom, from Jon Ronson, who wrote The Men Who Stare At Goats and is not the same person as Mark Ronson, who is a musician who makes all those records feat. Somebody Else. Despite not being Mark Ronson, Jon Ronson was once a musician in Frank Sidebottom's band, which is how he got the idea for a movie.
He explains himself in this Guardian write up; that he'd discussed the possibility of a film with Chris Sievey before he died, and had decided to write something about Outsider Artists in general rather than risk damaging the Frank Sidebottom, er, legend.
The movie begins, as in Ronson's real life, with "Ron" - played by someone who looks like one of the Weasley twins if the Weasley twins had been geeks - getting an impromptu gig with an unpronounceable band (the Soronprfbs) headed up ...heh heh... by a man in a giant cartoon papier mache head, which he never takes off. Not even in the shower. Ron is shanghaied into spending a year in a remote house in Ireland "rehearsing" for an album - the rehearsals bearing a strong similarity to the cult-abuse sessions held by Captain Beefheart for Trout Mask Replica - and eventually touring. The band take an instant dislike to Ron and want to kill him. Ron, for his part, is a starry-eyed musician who wants to make it big with his own compositions. He is hampered by his complete lack of talent.
At first (once I'd worked out this wasn't Frank Sidebottom we were following) I thought the band, and especially Frank, were a kind of figment of Ron's imagination, or at least just mythic figures, helpers and obstacles on his classic hero's journey to fame and and fortune. After a while, it became clear that it was actually a study in mental illness, and Frank (along with at least three band members, some diagnosed, some not there yet) was mad. Ron is our hobbit, our everyman, representing regular people by asking questions and reacting to situations. I didn't manage to figure out what Ron Jonson[*] (the real one) was trying to say about it, though. Genius is akin to emotional instability? We all wear masks to face the world? It's about getting into someone's head/getting out of your head? It was mildly affecting, and (it's billed as a comedy) I think I cracked a wry smile a couple of times, but overall it didn't click.
Ambitious Ron goes on to put the band's videos on YouTube (which they've never heard of) and books them into the SXSW festival. They travel to the legendary land of make-or-break-the-rock-n-rollers, as is de rigueur in all movies about modern music, to play the festival. Frank's anxiety gets the best of him, and things unravel rapidly. Frank is, however, back in his native country (how he came out of it in the first place is not specified) and so Ron gets to meet his Mom and Dad, who don't add anything to his mystique or for that matter explain any of it away.
Eventually, Frank gets his deeply peculiar mojo back, and it's Ron who melts away into the shadows.
It stars Michael Fassbender, Carla Azar, Maggie Gyllenhaal & Domhnall Gleeson - Carla, of course, being a real musician.
(This isn't very interesting either.)
[*] Edit to add: Oops. Well, you know who I mean.