If you live in the US, find a used copy at GameStop and then head over to TrueAchievements.org and take a look at the walkthrough someone put up there, it's written so that you will get each achievement as soon as the opportunity arises. It'll take about 10-15 hours to complete the game, then take it back to GameStop and tell 'em you didn't like it, and get all your money back.
I thought the game was alright, but I found the combat system is a bit broken. What I mean is that the game gives you weapons, but they aren't anywhere near as effective as just spamming the punches. I think that's why there are so many achievements for using the weapons because you'd avoid them otherwise.
At any rate, it actually picks up right where SAW
1 leaves off (it's even written by the same guys who wrote the first flick), which has it's ups and downs. The main character that you play is Detective Tapp (Danny Glover's character) who was shot in the chest by Zeb at the end of SAW
Well, the game claims that Jigsaw somehow manages to find Tapp before he dies and save him from the gunshot - that's a little thin. However, Jigsaw then traps Tapp in an abandoned insane asylum and tasks him to escape. Meanwhile, the asylum is filled with others that Jigsaw has set with their own task of finding Tapp to get the key to the traps they are set in. The catch is that Jigsaw put the key inside Tapps chest when sewing him up after the bullet extraction. Personally, I thought that was a pretty ingenious way of motivating the enemies to kill you, rather than them just being random lunatics. Having the enemies run at you saying "I need that key!" is actually pretty creepy.