Here is the full list of all 46 Saw achievements worth 1,000 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
Stomped five Minions to death.
Stomped first Minion to death.
Complete game using Truth Door.
Complete game using Freedom Door.
Kill the Pighead.
Release Jeff from his Trap.
First kill with a Gas Mine.
First kill with an Explosive Mine.
First kill with a Hatchet.
Release Obi from his Trap.
Used 20 Health Syringes.
Unlock 20 locked doors.
Release Oswald from his Trap.
First kill with Scissors.
First kill with a Gun.
First kill with a Scalpel.
First kill with a Table Lamp.
Release Melissa from her Trap.
First kill with fire
First kill with a Stun Mine.
First kill with a Shovel.
Killed a Collared Minion with a collar detonation.
Kill 20 minions.
Release Jennings from his Trap.
First kill with a Syringe.
First kill with a Nail Bat.
Kill 10 minions.
Used Health Syringe for the first time
Unlock 5 locked doors.
First kill with a Table Leg.
Idle for five minutes.
First kill with a Bat.
First kill with a Mop Handle.
First kill with a Mannequin Arm.
Release Amanda from her Trap.
First kill with a Crutch.
Died once.
Unlocked first door.
Unlock first container.
Find your first Patient File.
Kill first minion.
First kill with a Pipe.
Fought first NPC.
Find your first Asylum File.
First encounter with Pighead.
Complete Reverse Bear Trap.