They made Jigsaw too good.
He started off as a hypocritical, vindictive asshole who killed people over things like shoplifting and missing work. A really disturbed, messed-up character who made some good points and had a ton of depth as a result.
But as the series went on, a lot of that complexity got stripped away. His victims wemt from being normal people we could sympathize with to cartoon villains we were rooting to see killed. Jigsaw himself became this Liam Neeson-type antihero who was no longer a jealous old cancer patient lashing out at life, but a tragic father trying to avenge his son, getting into macho staredowns and action scenes...
He feels like a different character after 3. All I could think while watching the later films, especially X, was "This is the same dude who was kidnapping and trying to kill kids a few movies ago..."