It's far from perfect, I think they got a lot right, but probably went too far into "meta" commentary, which is somewhat what derailed Scream 4. This is closer to what that should have been. Very funny in parts, as far as horror jokes, not a SINGLE laugh from the audience I saw it with. ( who are these people that see Scream on opening night, and don't get any of the jokes?) I would have had a tighter direction, more style, more nods to horror greats in cinematography (too many shots just lacked style and life) and toned down some of the more laborious killing sequences. I also wanted someone to add a lot of realism, and this didn't really do that, which I knew going in.
They got me with killer misdirection, (though I did get parts of it right, very late in the game) although one could say that the film never really breathes enough to let the characters be and develop a little. They all toss of a lot of ironic commentary. It was almost too obvious, but that was the sleight of hand. Roger Ebert would say a movie like this doesn't really play fair as far as clues about the killer, which maybe misses the point of a slasher.
The Billy Loomis bits were almost out of a much, much worse movie. That was indefensible.
and regarding Scream 3, I always liked it. I am of the Scream generation, was 11 or so when I first saw it, and saw Scream 3 in theaters, which was really fun, to be that age when scary movies scared you differently than they do now. It's a little less edgy and missing Williamson's script, and does get a little silly in a spot or two, but most of it works. The whodunit is always questionable, and the last sequence was very Scooby Doo esque. That chase sequence in the movie set is probably the best meta commentary the series ever did, on some level, and as actual horror.