Based on the 1998 disappearance of Tom and Eileen Lonergan, it's the story of a man and a woman who accidentally get left behind in open water by their charter scuba tour boat.
It's scary, in the what-would-you-do sort of way, and because, while no one knows what really happened, they never came back, so it's basically a true story, the same way The Perfect Storm was.
There's a great attention to detail in the cinematography, and a dramatic and innovative use of lightning, and while the script probably won't win any prizes, it does capture the real-life conversations couples have. Early on, Daniel recites some facts about sharks, and Susan snaps, "Where did you learn that? Shark Week?" Later on, she's not feeling well, and the way that Daniel reacts is also quite realistic.
Still later, the couple starts arguing. "So now we enter the 'no talking' phase?" Daniel taunts. "I wanted to go skiing!" Susan retorts.
And when it looks as though they won't make it, they profess their love for each other. Perhaps not the best dialog or script...but it feels real.
And the sharks in this film are also real. No animatronics here. Which pretty much makes Jaws a nice little paddle in the lagoon.
(By the way...this is most likely the last movie of August, so, 8 months gone, I've seen 66 movies...the same number I saw in all of 2002!)