A seemingly abandoned boat drifts drifts New York harbor. When the police investigate they find a large rotting man who suddenly attacks them. Meanwhile on an island somewhere some over worked doctors are having to deal with zombies. The daughter of one of the doctors wants to go to the island to find out what happened to her dad. This is the movie with the infamous eyeball impaling and the incredible scene where a zombie fights a shark.
Also, according to his introduction on the blu-ray, this is Guillermo Del Toro's favorite movie.