(To preface, I will be referring to Angela using that name and as she/her considering that the sequels to Sleepaway Camp depict her as a transgender woman, not just as someone forced to live as a gender they are not.)
Sleepaway Camp left me speechless, and not in a good way. I was not prepared for how horrendous every aspect of this movie is. The acting is horrible in a distracting and laughable way from every single person other than Felissa Rose, the music is cheesy, the kills are creative but poorly executed and in no way scary, and despite some people's claims that the queer and trans aspects of the story are not offensive, I disagree wholeheartedly. This was 1983, I'd be shocked if the filmmakers were intending to explore queer identity in a positive light.
The beginning of the film shows John, a father of two, being killed in front of his partner, Lenny, in a boating accident along with one of his children. We're led to believe that Peter, the son, is killed and that his sister survived. However, it's revealed in a twist ending that Peter was actually the child who survived, and the female sibling was killed. Adopted by Martha, a mentally unstable aunt, Peter was renamed Angela and forced to live as a girl. This is depicted as being the cause of Angela's selective mutism, fear of water, and bloodlust.
Although I can understand the writers' idea that the trauma of Angela seeing her loved ones die violently would lead to her being mentally disturbed, the idea that her being raised as a gender she did not identify with would cause her to become a savage killer is ridiculous. Thousands of transgender people are raised as a gender they do not identify with, and this can be traumatic, especially if their parents are transphobic, but it does not cause them to become crazed killers. I can agree with the analysis that this theme is meant to explore the fact that raising a child to be a gender they are not is highly damaging, but as I said, it does not lead to violence. The result of Sleepaway Camp's twist ending simply seems intolerant and ignorant, using the image of a girl with male genitalia as a gross-out, shocking moment.
There is also a flashback that shows Angela and her brother seeing their father, John, and his partner, Lenny, share an intimate moment. It then shows one of the siblings reach out to touch the other on a bed, possibly in an attempt to reenact what they saw. Was the implication here that the siblings were sexually involved? I'm not sure since I haven't seen anyone talk about this scene, but the overall idea appears to be that Angela's mental state was negatively affected by seeing a romantic moment between her father and his partner, and possibly by engaging with her sibling sexually. Obviously, there are some homophobic themes here if my interpretation is correct, which is disappointing, but not surprising for the time period.
The only positive thing I can say about Sleepaway Camp is that the ending scene, which shows Angela frozen and snarling with her mouth and eyes wide open, is unsettling--not because of the twist, but because of Felissa Rose's incredible performance at just 13 years old. Having said that, Angela's character going from behaving normally the whole movie (other than being mostly mute) to snarling and rabid is odd. What about this particular moment makes her act this way? It doesn't make a lot of sense, but it is effectively strange and disquieting.