While parodies can be fun, biographies of real life people are always a little more difficult. A parody can sometimes reach into the realm of offense, but it's all done for the sake of a laugh and usually not mean spirited. Biographies on the other hand often go for sensationalism and therefore add a little too much fiction to the reality in order to create a "more interesting" story.
Nowhere Boy covers the section of John Lennon's life when he reconnected with his estranged mother. It also just so happens to be the same time when he met Paul and George and the Beatles were just starting. John spoke a lot about this time of his life, and many of the events are covered in the Beatles Anthology. But there is also a lot of sensationalism.
One strong element of the film is that John's Aunt Mimi, who raised him, is cold, strict, and basically averse to fun in all forms. When her husband dies near the beginning of the film, she shrugs off John's attempts to hug her in his grief, and later when she's angry at him she throws an apple and beams him in the shoulder. I've seen interviews with her before she died, and while you could say she softened in her older age, I can't see her ever being this ice queen. Paul McCartney reportedly also disagreed with this portrayal of her. It's done to create a strong contrast between Mimi and John's mother Julia, but that doesn't make it fair.
Julia on the other hand is a free spirit who loves rock and roll, let's John and his fellow bandmates drink and smoke in her house, and just all around acts more like a teenager than a mother. It's a little harder to say if her portrayal is accurate, as at least she never truly had the chance to speak for herself. Was she truly as bad a mother as she's shown here? It's hard to say. But since she's overall shown to be encouraging and loving to John in her own way, she doesn't suffer as much as Mimi does.
Despite these problems, I do think they do a good job of portraying just how lost and confused John was at this time in his life. Our relationships with our parents have a huge effect on us, and John was clearly deeply affected by the lack of his birth parents in his life, as well as the loss of his Uncle George, his surrogate father, and Aunt Mimi. He was a rebel and a bad boy, and music was pretty much the only thing that kept him focused. While he's certainly changed by the end of this film, he's still troubled, as he would continue to be even after the Beatles reached success. In that way, the title of the film is fitting and accurate.
While I expected a degree of inaccuracy, the one thing about the film that rubbed me the wrong way was the clear amount of sexual tension they included between Lennon and his mother. I don't think this was me looking into things the wrong way either, as some of the ways they would dance together or once as she leans close to him on the sofa just come off a little odd. On top of that, a bond forms between Paul and Julia, and the tension is there again, and John even seems jealous of it. Paul had lost his own mother a year before, so it's natural he might be drawn to Julia as well. Her death certainly built a bond between the two boys that could reasonably have led to them having the strong friendship they had, but they just took it a little too far at times and it creeped me out.
On the other hand, the part about the film I enjoyed the most was the music. It's a great mix of 50s classics from the likes of Screamin' Jay Hawkins, Buddy Holly, and Elvis, as well as covers done by star Aaron Johnson and a backup band called the Nowhere Boys. This is not a mix of Beatles classics, but rather rarities like "Hello Little Girl" and "In Spite of the All the Danger" which I've only ever heard on the anthology. It was nice to hear someone else sing those songs, and they did a good job of them. None of the actors look or sound like the Beatles, but they fit in well enough that it's not a jarring difference.
While this is a decent enough portrayal of John's youth, I'm not sure it would have much appeal to anyone other than Beatles fans. I could see showing this to someone to try to help them understand why I love John - that it's his flaws and difficulties that make me sympathize and relate to him - but I don't know if it's relatable beyond trying to understand John himself.