The follow up to "the chopped off foot seen round the world" Saw II was also not originally even a Saw movie, at least in it's earliest form. The script was reworked to fit the mythos far better than how a lot of franchises have done it, and it's got it's twists as well. But... science fiction movie reviews does it have enough of them?
Source: Saw II Movie Review - Decker Shado