When I wasn't laughing at the scenes of sharks leaping out of the water to attack their prey (in trees! on jetskis!) I was questioning the happy coincidence of a runaway motorboat heading directly towards a pier littered with flammable gas tanks.
Enjoyably trashy Jaws/Piranha rip-off, enlivened by likeable performances and some impressive 3D effects, but the plot is laugh-out-loud ridiculous and there's an oddly prudish approach to gore and nudity.
Lower any expectations you may have had, expect a flurry of terrible acting and chalky exposition, and 'Shark Night 3D' will deliver on a very minimal basis; it's dumb fun on the lowest common denominator.