In a sea (my big book of puns was handy) of bad shark movies, this one works.
This sort of plot you understand even before buying the DVD, if not... Just off-shore, a great white shark strands a girl on a rock. Simple. Most horror films are simple. What makes or breaks them is execution and this one is well executed.
The setting and filmography are first rate - this is a beautifully shot film. The special effects are terrific and the shark looks very real. The acting is solid as Blake Lively convinces as the film's hero. The villain (shark), again looks real, and is presented as the lurking terror that would scare anyone. The pace is steady and effective as the stakes continue to rise throughout.
This is a Hollywood monster movie so yes, the shark does a few things that are skeptically farfetched: knocks a whale twenty feet, catches on fire, bites through metal, and pursues a lone surfer like a vengeful stalker in a Lifetime movie. Most of those things I could also attribute to Jaws - so let's take it easy, lighten up, and not forget that we're watching a monster movie.
While this is not Jaws, this film contains enough to deliver what it should. A decent grab-the-popcorn, let's-take-scary-ride-and-be-entertained, what-if story.