Jaws is really two separate mini-movies, both about an hour long. First, there's the small town politics and hysteria dealing with a shark attack threatening the major industry of beach town. I gather that this section is actually the bulk of the novel, with many subplots that Spielberg eliminated (one involving the Dreyfuss character having an affair with Chief Brody's wife?!). The second is of course the drawn out three-man hunt for the shark aboard Quint's boat The Orca.
This is probably the first horror movie I remember being aware of. I was living on an island off the coast of Florida, and I guess I was 5-6 years old. We had to drive across the "3 mile bridge" to get to the mainland everyday, so as a kid, you spend a lot of time staring out into the water. This led to many "What if Jaws attacked the bridge right now?" scenarios and debates about who would win in a fight, Orca or Jaws.
This is the actual bridge to our island
As I was watching the original this time, I realized that I really haven't seen Jaws all that many times, for how famous and iconic it is. I almost certainly have seen Jaws 3-D at least twice as many times (a movie that still makes me wish I was a marine biologist working at Sea World). And it's definitely been many years .
So what makes it so great? It's not the shark, for sure. You don't actually see much of the shark due to all sorts of mechanical problems during filming, and Spielberg credits that with making him into a better filmmaker. Instead of showing the creature, he had to be creative in how he built the terror, which, coupled with the famous John Williams score, has become kind of a blueprint for screen tension building. And fuck, he was 26 when he started work on the movie. I don't think he's ever topped this one.
Of course, when I think of Jaws, I usually think of its legacy as the creator of the summer blockbuster genre. And that's a legacy I'm somewhat ambivalent about--for as much fun as The Avengers was, I often wonder how many great smaller films didn't get made over the past 35 years because the studios started putting all their creative muscle and capital into fewer and fewer "tent poles," many (most?) of which have been forgettable. Whatever, that's not Spielberg's or this film's fault. And really, the marketing around Jaws is really what set the template, not the movie making style itself, which as Pauline Kael noted, almost has elements of Woody Allen.
Incidentally, it just occured to me that I sort of owe my thon username to this movie--the SNL parody of it, rather. Google it if you haven't seen it!