The first one is a classic! not awful at all, or bad and cheesy... same for the other two. What is scary nowadays anyway... hard to make a scary film. The scream films were not meant to be full on scary...
As for a 4th, just leave the Scream films alone!! ugh.
Erm... not a lot to distinguish it from the first two, to be honest. It has its fair share of creepy phonecalls and the occasional stab or two. I sort of remember it in vague chunks... I know photographs of Sidney's mother were left at each crime scene. I remember there being a really underwhelming "big surprise" at the end, too.
I'm certain that photos were left behind in one of the films, and I'm 99% confident that it was the third one. I remember a scene where Dewey, Gale and Sidney went through them at the police station.
This is excellent news. I thought the first three were pretty good movies (no 1 will always be my favourite), and if they do re-hash the franchise for the 4th one I would be willing to give it a shot. Never say never, in my opinion.