Scream 3 is probably the weakest in the trilogy.
Again, it's cool that they reunite the cast. I like that they mixed things up with the beginning. Some of the new faces are super entertaining - see Parker Posey. And there's a couple of cool cameos, but one great one from the one and only Bianca.
Other than that, the story is super convoluted and it gets really annoying how they continuously try to make McDreamy look like the killer and then the reveal is a little bit naff after all the build up.
It goes on quite a bit longer than it should, most of the new faces are just red shirts and it bogs everything down. The music choices end up being completely bizarre, particularly towards the end.
So, overall, it's the weakest, but despite that, it's still OK and would have been a perfectly fine end to a trilogy.