WOW...
This movie was fucking awesome. If you're a fan of the franchise, and hated part 4, SEE THIS, it makes 4 look like a joke.
The only issue I had was that you have to have seen all of them for it to make sense. I was shocked at some of the stuff from past movies they went out of their way to allude to, but thankfully answered a lot of questions. Not exactly the most demanded ones, but some. There were a LOT of past flashbacks, more than in any other Saw movie, but I'd say it balanced well.
Also... the twists were really clever, though unfortunately, without spoiling anything, don't expect anything groundbreaking. Kind of like in Saw III, it was more about the surprise of what HAPPENS rather than the twist. "You Won't Believe How It Ends"... meh, going out of the way for a tagline like that, I guess that works if they're talking about what happens rather than some secret truth revealed. The twists mainly pertained to the film itself rather than the whole series.
AMAZING character development, no lifeless boring shit that was 4. Also the main storyline is kind of like Saw II but better.