47 Meters Down, a movie where actress Mandy Moore gets stuck in a cage 155 feet below the surface of the water and hunted by sharks, was initially supposed to go straight to DVD instead of hitting theaters. All of this might lead you to believe that it’s a cheap, dumb movie. It’s not. It’s actually a pretty good movie, in large part because it swipes way more from Gravity and The Descent than it does from Jaws.

The This Is Us star plays Lisa, and the movie opens with her and her sister Kate (Claire Holt) on vacation in Mexico. Lisa just went through a bad breakup, you see, and she wants to have a wild time south of the border to show her ex that’s she not boring. Kate, her more adventurous sibling, pushes her into going aboard a shark cage diving boat that looks just a hair shady. Once they’re in the cage, the winch holding it to the boat breaks, sending the pair careening to the ocean floor, 47 meters below the surface.

Trailers and advertising for 47 Meters Down would lead you to believe that the two girls spend their time fending off constant barrages of hungry, circling great whites, but that’s not the case. The sharks aren’t what makes their situation so stressful. That far deep, they’re running out of air, can’t get in radio range to contact the boat without swimming outside of the protection of the cage, and they can’t see where any sharks might be. The trailers are a lot brighter than the actual movie. It’s not a crystal-blue paradise on the ocean floor. No, it’s dark, with visibility so bad that they can’t see sharks coming until it’s too late, and if they swim too far into open waters, they can’t see which direction they came from. Oh, and if they wanted to just try to make a break for the surface, they couldn’t because they’d get the bends and die.

The sharks aren’t enemies so much as they’re just an element of what makes the real villain, the ocean, so scary. 47 Meters Down does for the sea what Gravity did for space and The Descent did for caves. These are alien places where people aren’t supposed to be (the floating debris in the dark water makes 47 Meters Down’s oceans look quite space-like, too). It’s not just that there’s something out to get you, but that you’ll die, alone, if you do nothing. Critics have noted that The Descent actually becomes less scary once the evil Crawlers start hunting the spelunkers outright, that’s how tense and stressful the setting is without the additions of monsters. 47 Meters Down is kind of like this. The shark-heavy third act is exciting, but not at horrifying as what came before it (especially because there’s a plot twist which may or may not work for you).

The similarities to Gravity aren’t an accident. (And indeed, there are similarities. Without giving too much away, there’s a scene where somebody sees someone who isn’t there due to a lack of oxygen, just like Sandra Bullock did.) Johannes Roberts even cites the film in a press release when he explained why there aren’t any cuts back to the boat on the surface one the cage falls. “Imagine if in Gravity, you kept cutting to ground control. It would have killed the movie.”

What actually kills the movie — or at least holds it back from being on the same level as Gravity — are corny, corny moments. There’s about 60 percent too much dialogue, and the characters constant narration of what they’re doing or what they’re afraid of undercuts some of the suspense. Not only does the audience wonder why they keep screaming about everything they’re doing while they should be conserving air, but it’s a big ol’ violation of “show don’t tell.” The terrifying emptiness of the ocean deep loses something when you fill it up with “Kate! Kate, I’m scared! Where are you, Kate! Oh my god, where are the sharks, Kate!”

Also, pretty much everything that happens before they enter the water is extremely deserving of the direct-to-DVD label. But, once the cage hits the seafloor, 47 Meters Down taps into the best, most stressful parts of the survival horror genre, surfacing for air only when Kate and Lisa take a mid-peril break to discuss Lisa’s ex-boyfriend.