It all comes together with the production design. You can see a lot of the money on screen as the different locations feel adequately dressed. Even the suits had an air of realism to them, something that usually doesn't happen in sci-fi movies. For some of these types of pictures, the CGI can be the weakest part with some low-quality stuff. But the VFX and all of that never looked bad. A large part of that success can be attributed to the dark setting, but that's an advantage.
Not everything was perfect as editing and story suffered multiple times, whether that included cuts that obfuscated characters doing actions, or glossing over details. That compounded with characters not having motivations other than trying not to die. Usually, there are subplots to give people depth, which causes you to hope for their survival, something that is absent here. The cherry on top was the decision to kill the black guy first. That is a little bit of a spoiler, but it's such a crazy decision that I had to point it out.
Overall, Underwater was watchable. If you find yourself needing something to see in theaters, then this could be it. I think that Kristen Stewart carries the film as the most interesting person involved. With its fairly derivative story, it's familiar but still rallies at the end. It's undoubtedly the best January horror movie I've seen.
I want the jacket that Kristen Stewart wears from the trailer