Like with Saw and other films relying on elaborate deaths via abstract/morbid means, there's only so many ways you can watch a person die before it gets. . . stale. I agree with others comments that at first couple of these were entertaining to watch, but then they start to get so utterly ridiculous due to the constant need to one-up the previous movie. I hadn't watched enough of them to know about the Tony Todd theory, though.

Excellent review of the series!

!1UP