The problem with the Jaws series is that there's not a lot you can do with a shark other than having it hang around a beach and attack people from time to time.
Jaws 2 is a decent effort as far as sequels go. It's a bit of a rehash, but has some nice set pieces and by focussng on Brody's paranoia adds something to the characterisation as well.
Jaws 3 is my least favourite. It has little connection to the other films, and was a poor attempt to breathe some life into series that had run its course (it was released in 3D if I remember rightly).
Jaws - The Revenge is simply one of the worst films ever made. And I meant that in a good way! It's got Michael Caine at his worst, and the suggestion that sharks somehow have a personal vendatta against the Brody family. It's as trashy as hell, but well worth a chuckle.