The Diary of a Teenage Girl is an odd film. It's often uncomfortable, and difficult to watch, but when the story centers around a 15-year-old girl who engages in a sexual relationship with a 35-year-old man who's dating her mother, you should be a little uncomfortable; especially if it's being depicted honestly, which in Diary it is. The film doesn't point fingers at anyone, it neither blames Alexander Skarsgård's character (the older man) nor Bel Powley's (the teenage girl), it's simply shown as something that has happened, and we're left to put the pieces together and decide how we feel about it, and what we think may have led Powley's character down this path.
Though the film is very serious, it's not without humor. The cartoon images that Powley draws in her notebook are often times humorous, while simultaneously disturbing. The film feels like an honest depiction of a teenager growing up in the 70s with no one who truly cares about her. It makes for a bit depressing view at times, but because Powley rarely gives into the depression her situation should inspire, you want to stay with her till the end.