There are other important innovations here, including the use of the camera to represent the shark's perspective, John Williams' oft-imitated menacing score, and of course the use of giant, scientifically inaccurate sharks as monsters in the first place. Even the cliched comparing-the-scars bit seems to have originated with this movie. Spielberg builds suspense and tension very well without resorting to too much gore or a high body count, and Richard Dreyfuss and Robert Shaw provide nice comedic counterpoints to stoic hero Roy Scheider. The animatronic shark, notoriously problematic during the shoot, doesn't hold up that well, but it's kept off-screen for long enough that by the time you see how fake it looks, you've already accepted its genuine danger.
I've never been a huge Spielberg fan, honestly, although I like many of his movies. He's a top-notch pop-entertainment filmmaker, but I can't remember ever being moved or transported or amazed by one of his films. This, of course, isn't meant as anything other than crackerjack genre fare, and in that sense it succeeds completely. But I admit I probably had a better time watching Deep Blue Sea.