Ivy Allie’s review published on Letterboxd:
The word that best describes this film is "beautiful." The visuals are absolutely exquisite. Freeze-frame this at any point and you'll see a perfectly-composed image with radiant, jewel-like colors. The set designs are superb, every one a slightly surreal but still completely believable environment.
The story is beautiful as well. It is, at heart, the basic love story, following in the footsteps of Romeo and Juliet, Pride and Prejudice, all the tales of star-cross'd lovers throughout history. It's a reverse Beauty and the Beast in which the beast is the captive. And like many of those stories, one of its central themes is that of finding the inner beauty of others, regardless of physical appearance. This may be del Toro's most deeply human film, even if it is centered on a fish monster.
But if the film is about beauty, it's also about ugliness. The villain is human cruelty made flesh, a being of absolute hatred who can and will perform the most heinous acts imaginable. Characters who attempt to do good are punished mercilessly for their trouble. All of our protagonists exist on the margins of a society that has deemed them unacceptable for ultimately trivial reasons. The theme of ugliness is visible even in the basic setup of the story: this shimmering, unique creature chained up in a cold basement so that a few bureaucrats can use it as a pawn in their meaningless arms race. This dual theme has been present in much of del Toro's filmography at this point but it's rarely been more pronounced than it is here.
I'm not going to deny that the film has some off moments here and there. It's not perfect. But it's probably the closest that del Toro, or perhaps anyone, has come to nailing that concept of the "modern fairy tale," and I for one really love it.