This movie is not the next "Jaws", and it is not your typical scary shark movie. It's more than that. There is very little gore and no actual violence (that is seen). There are some surprising and startling parts of this movie (when the sharks fins crop up out of the water), but you won't be white-knuckled for most of it. Think of it as more of a drama/suspense, not an action, scary or horror film. It's more about the couples' war between themselves.
It is still very scary, but a different type of scary: tense and psychological. Much of the tension is only in your head. You will ask yourself "where are the sharks?". As Daniel Travis says, "I don't know what's worse: seeing them or not seeing them."
Director Chris Kentis filmed the movie with a digital, hand-held video camera (giving it a "home video" type of feel). Also, this movie was very low budget, so Kentis couldn't afford any Spielberg type of special effects. So what did he do? He took the actors and dumped them into real shark-infested waters! Therefore, you can sense that some of the actors' fears are genuine. These two things make the movie very realistic.
PLOT/SCREENPLAY: The couple, played by the unknown actors Blanchard Ryan and Daniel Travis, go on vacation. On their vacation, they go scuba diving, and after a miscount, are mistakenly left all alone, in the middle of the ocean. They tread water for most of the movie, talking to themselves and watching for sharks. The couple try to live through jellyfish, bouts of vomiting, and themselves.
I was impressed with the plot. It's a rather simple one, but I felt the script did a lot more with the plot then I had expected. The plot's basis was based on a true event, so that makes it all that more scary. The only problem with the plot is that the end is somewhat anti-climatic.
DIALOUGE: The couple have nothing else to do but talk to eachother. The dialogue shows their moods shift from optimisitic, depressed, angry, in denial, casting blame on one another, tired, hungry, and finally submissive.
Some people say the movie didn't tell us enough about the characters for us to care about them, but I disagree. The dialogue helped to develop the characters and give them depth (make them seem like real people). The dialogue also helped the plot to extend over the course of 79 minutes without wearing thin. It's also very interesting to see that the dialogue shows how their moods change.
ACTING: As aforementioned, some of the actor's fears are genuine (since the sharks were real), so there's no problem believing the actors are scared, but when the actors change (and become angry and depressed) you can really feel what they're feeling. It may be partly due to the "home video" feature (which helps to capture the atmosphere), but the viewer almost feels like you are stranded in the ocean with the actors.
In conclusion, this movie was very well made and I recommend it (especially to "Jaws" fans, even though this movie is not very much like it). I also recommend it to fans of psychologically scary movies. It is not for those that are easily scared; it will make you never want to go into even the swimming pool again.