Actually, I liked Scream 2; thought it was about the best sequel that could be made from that particular material. But Scream 3 just...flat...sucked.
Part 4...well...it didn't suck necessarily, there was just absolutely nothing new about it. And when you're a franchise pushing twenty years old, new is what you need.
I love the Scream franchise, on of my favourites. 3 did border on horrendous but it's fun to watch when there's nothing on TV. 4 I enjoyed but it wasn't as good as the first. I'd probably watch the series if I got MTV but I don't think it'd ever be good without the original cast.
Let's not forget the 'Teen Wolf' series that basically added all this weird show mytho and magic mumbo jumbo. Not all MTV shows can be bad though, I remember the Spider-Man cartoon on MTV being pretty decent and I thought it was a cool way to tie in to the Raimi movies.