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.
Complete Reverse Bear Trap.
First encounter with Pighead.
Unlock first container.
Kill first minion.
Used Health Syringe for the first time
Find your first Asylum File.
Find your first Patient File.
First kill with a Pipe.
Fought first NPC.
Release Amanda from her Trap.
Release Jennings from his Trap.
Release Melissa from her Trap.
Release Oswald from his Trap.
Release Obi from his Trap.
Release Jeff from his Trap.
Kill the Pighead.
Complete game using Freedom Door.
Complete game using Truth Door.
Kill 10 minions.
Kill 20 minions.
Used 20 Health Syringes.
Idle for five minutes.
Died once.
Killed a Collared Minion with a collar detonation.
First kill with a Mannequin Arm.
First kill with a Bat.
First kill with a Nail Bat.
First kill with a Mop Handle.
First kill with a Scalpel.
First kill with a Syringe.
First kill with a Table Leg.
First kill with a Crutch.
First kill with a Shovel.
First kill with a Table Lamp.
First kill with a Hatchet.
First kill with fire
First kill with Scissors.
First kill with a Gun.
First kill with an Explosive Mine.
First kill with a Stun Mine.
First kill with a Gas Mine.
Stomped first Minion to death.
Stomped five Minions to death.
Unlocked first door.
Unlock 5 locked doors.
Unlock 20 locked doors.