I did not entirely dislike this movie. And that is not a promising way to start a review.
The story is kind of beaten to death - do not expect significant twists and turns along the ride for like 99% of the movie. What i look at very much in horror movies is "how the protagonists communicate with each other". How do they tell each other about the things they have seen, heard, experienced. For me - a horror movie succeeds or fails with the communication. When the protagonists act idiotic and simply leave out the crucial facts - while chatting away in vague terms only - the best story and visuals cannot save it.
In that movie - the communication between the protagonists was ... alright. It certainly was not perfect (far from it) - but then again - the movie does not go into sufficient detail about the relationship of them. However - considering they are siblings - i did expect more empathy - even for siblings that became estranged. All in all though ... it is still "ok".
Another factor about the communication between them and that it did not feel quite good - was the acting. At times i felt thrown back to an 80s or 70s horror flick with its immense overacting. In short - i really, REALLY did not like the acting at all. It was not high school level bad - but it was very low budget bad.
The practical effects were good enough - but the movie did not demand much anyway. The CGI effects or other visual trickery was pretty bad.
Why was it still a 4/10 for me then?
It was consequential and did not fall for a typical resolution. I value this very highly when it comes to movies that usually follow very strict parameters.