Look, I can understand the basic premise... Some dude has a couple crossed wires upstairs and starts trying to make people appreciate what they've got by taking it away. It's an interesting concept, I'll give it that.
But the way the movie goes about presenting that concept is absolutely ridiculous. And those traps are stupidly elaborate and resource-consuming, he'd have to spend weeks setting up just one of them in only the most basic version. Admittedly, a serial killer would probably have the patience to do something like that, but they're still just silly.
Jigsaw turned into more of some weird evil demigod or something. With access to any kind of material or chemical, whatever labyrinthine dungeon he wished, and whatever victims he might choose to stick into his batshit contraptions.
All while remaining unconscious! Now, even I've got to admit that that's pretty impressive.
It's all just so silly. It's unbelievable. Oh, sure, it'd like to instill us with the fear that some madman is going to put us into a sadistic rat race for our lives if we don't appreciate what we've got and in general not worry and be happy. But by the time he's researched me enough to know my patterns and my particular "sin", has located an abandoned basement or something to hold his games in, has imported the various materials necessary to construct his diabolical deathtrap, and finally assembles the damn thing (while of course covering his tracks impeccably and securing multiple escape routes for himself, all covered by equally complex traps which he of course remembers the exact location of and/or the method of getting past it unharmed), then I'll be so old that I'll save him the trouble and drop dead of natural causes.
Deep down inside all the gore, all the torture, all the poor acting, all the hilariously bad and disconnected writing, there is indeed a basic premise that's kind of intriguing. But it's almost impossible to see that.