Jigsaw's whole Crazy-Prepared scheming, really! Over the course of his "career" as a killer, he made progressively complex plans to continue working that eventually involve around his exact predictions of how other characters would behave at certain points, deliberately getting himself into risk of being arrested, or to put his apprentices and accomplices into judgement, culminating in factoring his own death in a single game. And all of those schemes end up being successful, even staying in motion long after his death until some time before the events of Jigsaw. One would deserve to be tested by him if they don't give him credit for achieving all of this.
Whenever you see a protagonist survive at the end of a movie (or anyone for that matter), it's pretty awesome, considering the franchise's iconic Anyone Can Die complex.
At the beginning, Eric manages to escape the Bathroom after the second film by breaking his own foot. A flashback near the climax builds up on this by revealing that he caught up to Amanda and delivered her a brutal Extreme Mêlée Revenge. Even after she gets upper hand on him by kicking his broken foot and walks away, he taunts her by shouting that she's not the real Jigsaw, effectively hitting her Berserk Button.
Lynn's short, but effective "The Reason You Suck" Speech to John, when he asks her how people will remember him.
The Spike Trap is equal parts terrifying and awesome. An older couple, Morgan and Rex, are chained back-to-back on a metal pole with spikes driven through their bodies. The spikes pierce Morgan's body at positions she'll heal from, while Rex's pierce through major blood vessels. Rex has been horribly abusive toward her and their daughter, to the point of causing her multiple fractures, and Jigsaw's tape asks her to finally disconnect herself from this horrible man. As soon as it ends, and with just a moment of hesitation at the start, she rips the spikes out one by one.
John: You think you will walk away untested? I promise that my work will continue, that I have ensured. By hearing this tape, some will assume that this is over, but I am still among you. You think it's over, just because I am dead? It's not over. The games have just begun.
The Reveal that Logan is the Jigsaw Killer, swiftly followed by them killing off the guy you thought to be the killer, is quite the badass introduction to our new Jigsaw.
The Serial Escalation with the traps. We've gone from rusty scraps and barbed wire to collars mounted with laser cutters.
After finding out what a horrible bitch Anna has been (killing her own baby and then framing her husband for it which led to him killing himself, all without a hint of remorse), seeing her brains blown out while trying to kill Ryan is utterly satisfying.