I'm not a fan of Jehovah Witness after my wife was harrassed on the door step and had to call the police to get rid of them. I am also not particularly religious but I still enjoyed this film. Although this obviously has a great deal to do with the religion, at its heart it really is just a coming of age film.
The film follows Gabe and his friends as they try and be teenagers while following the strict religion that punishes them with not being allowed to interact with other Jehovah Witnesses. Of course being teenagers they break all the rules.
This is not a religious film. There is sex shown and mentioned but nothing explicit. Although there is a comical but explicit integration of a new adult recruit about accidental anal sex with his wife. I wouldn't watch it with your nan.
Overall I enjoyed this film. There are funny and sad parts. The film showed the harsh realities of being a Jehovah Witness but at the same time did not preach that people who choose this religion are bad or stupid people. The film has moments with older Jehovah Witnesses about why they joined the religion. Although it doesn't make it clear if these were genuine or actors.
The whole Jehovah Witness thing may put people off but they are missing out on a decent film. The film is basically a coming of age film just with the twist of being set with the turmoil of a religion that frowns upon all the urges and things you want to do as a teenager.