The Jaws NES game did not nearly follow the original movie that it was based on, but the development team did seem to have put some thought into the game's basic premise. Why then are there a sufficient number of people who do not like this game? The answer, my friend, is found not in the premise of the game but in the execution.
The idea behind the game was to allow your character to gradually build up enough strength, RPG-style, until he is finally able to destroy Jaws in an encounter with the beast. The execution of the game had you killing off simple stingrays and jellyfishes in numerous mundane encounters in order to collect enough shells to buy a receiver/radar and additional power. There was the occasional encounter with a baby Jaws that would sometimes allow you to participate in a bonus round to collect even more shells. When you finally do encounter Jaws, you'll find that he isn't very menacing and that, unless you have a sufficient amount of power, you'll have to shoot the creature nonstop until you're suddenly and unexpectedly taken back to your boat for no apparent reason in order to find even more stingray/jellyfish encounters as you still await another encounter with Jaws, who has somehow restored a good portion of his energy. Oh yeah, and then there's the final encounter with the beast, but maybe I've said too much already.