It's Lars Von Trier-level miserable here- completely unrelenting and deeply upsetting at times. It would be easy to resent the film for this and dismiss it but the cast give such compelling and rich performances that you allow yourself to become invested and you, basically, let the film make you feel like crap.
Set in bleak suburban England, literally everything about this picture is bleak and unpleasant. Enough of this is justified, however, through the movie's focus on emotional abuse, as much as physical abuse. The film's look at masculine aggression in particular is extremely impactful and completely justifies sitting through it.
It's a side point but, I must say that I really liked how the title of the film came up in the story- I was hoping that it would and it's brief mention actually resonated with me a lot so, bravo,
Anyway- not for the faint hearted- 'Tyrannosaur' will leave you feeling sick but not every film is sunshine and rainbows, nor is every life, unfortunately, as is shown here.