It's been a while since I saw Saw...
But as I recall, it was derivative, discomforting*, and hyperstylized (for no good reason). It had characters who at times struggled to approach one dimension, an extraordinarily manipulative plot, illogic and plot-holes up to its metaphorical ears, and a particularly bullshit moral.
*"But Malice, horror films aren't necessarily supposed to be comforting!" Yes, but there's a difference between proper tension
, even claustrophobia
, and what Saw does, which is (if I recall correctly) a very manufactured, grimy tension, a closed-in feeling of contrived nausea. I know I was sick to my stomach, watching it, and I'm not normally affected that way by movie gore.
You could easily claim that Se7en is, among other things, a set-piece movie, as centered on the 7 grisly murders as Saw is on its death-traps. However, Se7en takes those set-pieces and connects them within and between them with real, 3-dimensional characters, a meaningful theme (as opposed to Saw's closing, apologetic folderol), a consistent and proper tone, and a related and appropriate visual strategy.
It's kinda the difference between saying, "Boo!" and saying, "Look at what humanity is capable of. Smell this rotting flesh, sense the weight of endless sin and hate, and recognize that it is within you, too. Madness feels like velvet."
Both of those statements are scary, sure. One of them is better.
And hell, it isn't even a very good "Boo". I don't expect a movie like Saw to be a great work of art; but if I'm feeling ill I'm not feeling scared, and if I don't care about the characters I'm not going to be afraid for them during a goddamn shootout, and if you end your movie by trying to apologize for what you've done it's going to piss me off. The tools of filmmaking can and should be aligned for the creation of art, but that doesn't mean a piece of schlock entertainment can totally abandon them and still be effective and fun.