Of all the films that I've watched over the years...
...this is the one I feel deserves a remake the most. There's tons of potential here. The premise of the divers having to swim only a small distance for their safety while confronted with a hungry shark is simply wonderful. The simplicity of the premise and the lack of resources for the characters can make for an incredibly tense and unnerving experience.
Besides the premise, the shark shots were realistic and frightening (and could be again), the build-up was great and the continual looking below the water made for quite a bit of suspense. A remake could be the shark film that we've been waiting for since Jaws.
HOWEVER - the film as it is now is severely lacking. The acting ranges from poor to atrocious, the back story of the characters is laughably clichéed and shallow, the dialogue is something from kindergarten, the ending is unrealistic and pretty bad (though opinions differ on this) and apart from the shark shots, the whole thing looks poor.
With better dialogue and backstory and a competent director, I think this one could be great. Perhaps a different, more aggressive shark? What would you like to see in a remake?