At a vast, tunnel-filled underwater laboratory somewhere off the coast of Mexico, a trio of supersharks swim around, their brains genetically enhanced by a research project that has something to do with curing Alzheimer's. (The less said about the logic of this experiment, the better.) These nasty, machine-mouthed specimens aren't just cleverer than your average set of jaws. They're faster. Smelling blood and flesh, they cruise through the water like heat-seeking torpedoes, arriving at their targets with a frightening sense of purpose. At one point, after the sharks have begun to destroy the lab and consume its inhabitants, one of the apparent heroes delivers an inspirational, let's-keep-it-together speech, thick with clichés, and just as he's hitting his stride -- chomp, he's shark meat. The formulaic screenwriting almost becomes a knowing joke. It's as if the audience had been set up for the kill.
As ''Jaws'' knockoffs go, ''Deep Blue Sea'' is certainly far superior to ''Lake Placid,'' a cardboard ''spoof'' that makes even the amusing tackiness of ''Anaconda'' look like high cinematic style. That said, this is still the sort of movie that delights in turning its actors (they include LL Cool J, Saffron Burrows, and Samuel L. Jackson) into saps so that we won't do much more than shrug at the prospect of their deaths. Harlin works on a pleasingly explosive scale. The many propulsive shots of cascading fireballs, metal walls being battered down, and actors in waist-deep water trying to keep ahead of ominous gliding fins end up spinning you right past the minor detail that the sharks have far more personality than the people they're eating.