Catharsis Factor: Following The Reveal of Anna's killing of her baby and framing her husband with no regrets, seeing the selfish sociopath getting hers when she tries to kill Ryan is absolutely satisfying.
Critical Dissonance: Only 34% of critics liked it on Rotten Tomatoes, but a whopping 90% of audiences liked it.
Magnificent Bastard: Logan Nelson is revealed to be the first apprentice of John "Jigsaw" Kramer, having been one of the people selected for one of Jigsaw's first games for accidentally mislabeling his X-ray. Saved by Jigsaw from death when he realized that Logan didn't deserve to die over an honest mistake, Logan assisted Jigsaw in his games, even helping build the infamous Reverse-Bear Trap. Ten years after Jigsaw's death, Logan proves himself to be a worthy successor to his mentor by successfully framing the corrupt Detective Halloran as the new Jigsaw killer; orchestrating a reenactment of the game he was chosen for, using criminals let off by Halloran; planting evidence against Halloran in his house; and finally trapping and killing Halloran himself, but not before getting him to confess to being responsible for the loss of innocent lives, including Logan's wife.
The Reveal that Logan is the new Jigsaw is initially somewhat shocking, but it's immediately followed by an extremely lengthy Infodump that completely disrupts the scene.
Logan's plan. Framing Halloran by recreating the game in the barn, down to picking out Halloran's informants that looked similar to the actual victims... when no one had even discovered the previous game to begin with.YMS summed it up perfectly:
They Wasted a Perfectly Good Plot: The film's poster and viral marketing campaign would have you believe it deals with the lingering influence the Jigsaw games have had on society, with the antagonists being a cult-like group who are carrying on their "savior's" work. Instead, this is only mentioned once as a fansite, and the twist is basically a repeat of previous entries, with yet another apprentice who has somehow been working with John the whole time. The twist that the main game is a Stealth Prequel to the entire franchise also renders the whole thing inconsequential and makes you wonder if this is really a story that needed to be told.
The villain, Ray Cathode, makes his debut with his head stuck in a TV box.
Everything about Mr. Noseybonk.
The Scrappy: Mr. Noseybonk. Not only is he unintentionally nightmarish and off putting, he annoys innocent people minding their own business and generally acts like an obnoxious six year old. One IMdB user recalls how Mr. Noseybonk still haunts him to this day.