Well I guess if anything Saw could use 3D effectively. I'm not really interested personally though.
I first saw (heh...) Saw 2 and enjoyed it, then Saw 3 and hated it...killing the series for me until I saw the original Saw, prompting me to watch Saw 1, which was great. That third one's still killed the series though from my perspective, it just turned into torture porn instead of thriller/horror, and from what I hear it doesn't sound like it's ever gone back.