Scream 4 should have been terrible - after all, Scream 2 was only "ok" and Scream 3 was a disaster. But Scream 4 is a very good movie, both as part of the franchise, but also as a stand alone.
It is far more self-referential than you would expect. Barely a scene passes without the characters referencing movie conventions. But it does so in what I think is an intelligent way. And most importantly (for our enjoyment) Scream 4 makes fun of itself before we can get there. Just when you start to roll your eyes, they roll their eyes.
But it also stands as a good slasher flick - perhaps the LEAST slasher-y of the lot so far (it can't be everything after all) but there are plenty of jump-in-your-seat moments.
The combination of old generation cast and new generation is actually seamless, again lots of self-referencing about that too.
The highlights are too many to name - but the opening of the movie will have you laughing far harder than you'd have expected to.
Overall, Scream 4 is excellent.