
You ever watched a movie like this and go "wait, this movie took a complete left turn here". Yeah, exactly. Though, the subject matter that the movie is based on, fairly helps to comprehend what kind of a story will play out. Anyone else watching this blindly, will be surprised by the how the plot unravels from a kinship to, well, teenage manslaughter.
This is one of Peter Jackson's weirdest projects, right before he went to the mainstream, directing The Lords of the Rings trilogy and King Kong remake. But if you've seen his early filmography, so much of that is right here. Of course, with the exception of award winning performances and talents of rising stardom like Kate Winslet in the film. But this film is unlike anything I've seen. You don't know whether to believe in the characters or not because they take into some weird, twisted downwards spiral later on.
Warning: If you don't want spoilers, there's going to be some details revealed about the film. If you want to go in blind, might want to be careful about what you'll read next. Am not going to reveal the entire plot. But, with the reference I'll give, it might.

Heavenly Creatures is a movie based on the Parker–Hulme murder case in Christchurch, New Zealand in 1954. Kate Winslets plays as Hulme, a 13-year old girl from an affluent family in London, who came to study in Christchurce on a temporary basis, she befriends Parker, a 14-year old girl native from New Zealand. Hulme is a precocious student who likes to tease, and belittle her teachers while being completely free spirited and free. Seeing her sunny disposition, Parker, who seems to be the socially awkward type, follows and both eventually play around, having stupid fun. Which kind of becomes their own little curse.
Both of them eventually develops a friendship, but one that kind of swirls both their parents into bigger problems as well. These two are so close, they'll do whatever it'll take to not separate from each other. Unfortunately, this isn't a Disney movie. There's no wonderland they can actually escape, despite how much they daydream about it. Both of them wants to leave for the US, where they can live their dreams of being famous. Hulme wants to be an actor, and Parker wants to be a musician.

The film explores darker themes like sociopathy, psychopathy, envy, depression, same-sex kind of relationship that transitions to a complete dark turn. But despite these people two being the center of the character study movie, a lot of the people you see in the movie are also painted as provocators, that have led them both, mostly one specific character, to their boiling points.
This is a crazy film to watch, almost everything is just in this hyperactive dream state. You get so much shots of these two acting like complete juveniles, not even having a little bit of decorum. Am talking about actors on the screen. It's like they were given free permission to go buck wild. Entirely. There's this nice, lowkey haunting, ethereal atmosphere set up around the later act, that cerebrally prepares you for what to come.
This is a fun movie, if you're really into character studies. It is choke full of surprises. So many facets to look, how different people with their own biases affect one another. Peter Jackson kind of outdone himself, and I can see why he was picked as the director for TLotR. You won't like everybody, but you understand where they're coming from. Some characters you symphatize with because there's nothing more they can do to control the situation, bring a better outcome, only doing what they know best.

To Sum It Up
This is one of Jackson's greatest classics, really underrated. Just like Bad Taste and Braindead. He even made Freighteners with Michael J Fox, that was his only mainstream film in the 90's before then.
He does horror and comedy both well together, sometimes mixes both of these into psychological dramas or epic fantasies. To be honest, I kind of miss dreamy Peter Jackson films. He went to the wayside after directing the Hobbit films. These days , directing WWI documentaries and something about the Beatles.
This movie was nominated for Oscar for best screenplay, of which credit is shared to both Fran Walsh and Peter Jackson. Subsequently, Jackson won his Oscars from the third Lord of the Rings film. 3 of them to be exact. That explains how everything flows into the film, seemlessly because the screenplay was holding your attention.
If you're into weird films like this, that gets a hold of your attention and manages to catch you off your guard with so many odd developments, then do check this out.