The premise couldn't be simpler. Nancy (Lively), by way of honoring her late mother, travels to Mexico to surf at a very specific beach. The secluded spot was the very same one her mother surfed while pregnant with her. Kind of a secret, 'locals only' nook, Nancy finds herself nearly alone. There are a couple male surfers nearby who beckon her to join them, but Nancy isn't looking for flirtatious dudes. Much to everyone's dismay, a great white shark has infiltrated the shallow waters and quickly begins eating its way through everything in the area.
Nancy is among the attacked, but she's lucky enough to get away—not unscathed, however. She has a very severe bite wound on her leg. Her goal is simple, but seems simply impossible: make her way back to shore without becoming shark food. The shark isn't going anywhere, so Nancy is stranded on a very small rock (as miniature an island as you can imagine) a few hundred feet from safety. She's not quite alone. There's a wounded seagull sharing her rock. The bird gives Nancy someone to talk to, sort of like a slightly more animated version of Tom Hanks' volleyball Wilson in Cast Away.
In other words, if you saw the trailer you basically know what to expect. Plot twists aren't the point here. This is a harrowing story of perseverance. The resolution gets a little out of hand, with director Collet-Serra amping up the horror/thriller antics more than what's really needed. Remember how subtly writer-director Chris Kentis' Open Water (2003) covered similar territory? (If not, rent it—it's definitely worth a watch!) Sometimes more is less, and the climax is the one stretch where Collet-Serra loses his sense of relative minimalism. And even then, it's still pretty exciting.
Sony's Blu-ray (which comes with a really cool lenticular slipcover) offers outstanding audio/visual presentation. Surfing is among the most photogenic of sports (and Blake Lively is among the most photogenic of actresses), so the super-sharp 1080p transfer of Flavio Labiano's cinematography is much appreciated. The audio is offered in DTS-HD MA 5.1 and is a great study in contrast (the quietest scenes are unnervingly quiet, but the lossless surround mix packs a punch when needed).
Special features include a few deleted scenes and four featurettes: the making-of "Shooting in the Shallows" (six minutes), "When Sharks Attack" (eight minutes) featuring a real-life shark attack survivor, F/X special "How to Build a Shark" (seven minutes), and a look at the shooting location in "Finding the Perfect Beach: Lord Howe Island" (six minutes).
With tension to spare and even a little character depth (with Nancy expressing second thoughts early on about her plans to become a doctor), The Shallows is worth the time.