At the start of the movie it's not clear what is going on, but everything seems creepy because of the editing, the camera work, and the music.
I have seen Robert Englund, but I don't recall whether I've seen him as a horror movie villain, and I certainly haven't seen his trademark role. He is outstanding here as a villain, and now I want to see him in the other role. Here, he is creepy but calm and intelligent, sometimes friendly, occasionally funny, rarely angry. I'm not saying I was rooting for him, but Stuart is the type of villain one is tempted to see succeed.
Emily Berrington does a good job as well. She's pretty and adorable but slightly edgy and quite tough. We don't actually see that much of her, and much of the movie is a cat and mouse game involving Martin and Stuart. Finn Jones is capable of handling himself, but it is a challenge.
Malachi Kirby is tough as a boss when he has the authority, but in a crisis he's more of a coward. That still could mean a good performance.
I don't know the name of the police officer in charge, but he's really good.
There is some violence, but mostly the movie is very tense. It's effective as a thriller. There are so many challenges to be met.
I'm not a fan of horror, but this was really good, mainly due to Englund.