Underwater opens with an earthquake destroying a research/drilling facility miles deep in the ocean. Led by their captain (Vincent Cassel), the survivors (Kristen Stewart, Jessica Henwick, Deadpool‘s TJ Miller) must get out of the rubble and walk across the sea floor to be able to get to the remaining escape pods in another station. Kristen Stewart plays the engineer, she fixes things, computers, back up power, UPS, etc. Jessica Henwick, the scientist, and TJ Miller, the comic relief. He provides the punch line about a missing punch line in the movie.
Some would say Alien in Mariana Trench. You can take that as a knock and compliment both. The plot may be recycled from this and that movie but as a horror film, it works. I think the setting is one of the reasons why. We’re more familiar with the outer space, zero gravity, space walk, etc. than with the ocean floor and its mostly unseen creatures (unless you’re into Animal Planet). Real sea creatures are sometimes even more “alien” and scary than the fictional space aliens. The sight of a huge octopus can be just as alarming as that of the algae-like thingies floating in the dark of the ocean.
Walking on ocean floor in bulky pressure suits where you have you limited movement and visibility? Good luck with that. You won’t easily see if this ugly sea creature is floating just from behind your back. On the plus side, you have to strip to your underwear to fit in to that pressurized suit. And TJ Miller in his tattered boxers is a sight to behold. Some may have complained that some scenes are too dark and/or that the action scenes are a bit confusing but that is actually the point.
Underwater has a B-movie plot, but it gets an A for atmosphere (atmospheric pressure?) and VFX and maybe, C for characterization. It delivers on cheap thrills, if that’s what you’re after. And for movie that’s set in the vastness of the ocean, there are moments where it managed to be so goddamned claustrophobic.