This one was meh. The movie itself doesn't look cheap โ it's an Amazon movie with a real studio behind it โ but the plot sure feels that way. One review summed it up as "the standard shark vs. idiots storyline we've witnessed a dozen times over" (We've Got Back Issues), and that's about right.
The setup reminds me of The Descent (2005). That movie still scares me โ the idea of being stuck deep in a cave with no way out is one of the worst things I can imagine. The Devil's Mouth wants that same trapped feeling, but it never gets close. Next to The Descent, it's nothing. One critic called it "a cross between The Shallows and The Descent" (In Review Online) โ I haven't seen The Shallows yet, so I can't speak to that half, but the Descent comparison checks out.
And the shark? Classic bait. It's there to put a monster on the poster, not because the story needs it.
Skip this one, and if you have not seen The Descent, watch it!