Robin Solsjö Höglund’s review published on Letterboxd:
A Monster Calls is a drama with fantastical elements, about a young boy, Connor, who deals with his mother's fatal illness by beginning to imagine a massive monster at his side.
This looked interesting because it has that Pan's Labyrinth sort of thing going, but it's not too similar to that. It's more like a Where The Wild Things Are. It is mainly a pretty heavy-handed drama, but I think it can be a good film to show to children (not the very youngest) in helping them come to terms with how they are feeling about life and loss, sadness, anger and death. In that regard it's not too bad, but just as a standalone film experience it leaves a lot to be desired for me.
There's a good cast here though, the mother is played by Felicity Jones, and her mother by Sigourney Weaver (doing a British accent, that's new) and the monster itself is voiced by Liam Neeson. The special effects hold up very well, and my favourite aspect of the film was when the monster told the boy stories, which were often shown as animated sequences.
I think this one is basically intended for younger viewers (anywhere from 9-13?), and people who are addicted to tearjerkers. It's just not my cup of tea overall, but that is definitely not to say that it doesn't have good, even wonderful moments in it. It just hammers very hard on a single concept and idea, "boy deals with pain and sadness by inventing monster" and the tone is weepy and tries a bit too hard. I just wish it were more nuanced and had more things going on, but as a whole it is not entirely awful either.