This movie fills the void of the franchise by basically creating a Prequel to the entire storyline (taking place technically between Saw 1 and Saw 2). This film helps build a backstory for John Kramer's story, but that's about it.
The traps are Minimal, Very predictable & not brutal at all (Except trap 3: where a woman needs to sacrifice her legs for her head to survive - that one was very entertaining). There's only about 7 trap scenes in total and one of the scenes is made up in Johns head at the beginning of the film, so technically that would make about only 6 traps with the final (6th) trap being a staged setup for two.
The ending was very unsatisfying because of the way it played out and the fact that the "Villain" of this film doesn't actually get the cut.... I won't go further as that would basically spoil the film... but yea... The best way I can explain and describe this movie without giving out a complete spoiler is that the film ultimately shows John Kramer as a sympathizer, which was completely unexpected....
As a huge fan of the Saw Franchise, this movie was needed to complete the saga (wait until you see the ending to see what I mean) but, I feel like maybe it could have been ALOT better if James Wan & Leigh Whannell (The original creators of the series and the reason why Saw 1 - 3 was so damn successful in the first place) was involved with the production and writing. This film also, unfortunately has the weakest acting from Tobin Bell out of all the movies in the series, which is a bummer. The acting from Shawnee Smith (the actress that plays Amanda) was also pretty lackluster TBH. [3 out of 5 Stars]
TLDR: it's worth a watch just for the sake of completing a long running franchise story, but far from what a true Saw masterpiece should be. (PS: Stay to the end of the film for a secret ending.)