Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

The Easy Way (100 points): Complete game in easy difficulty.
The Normal Way (150 points): Complete game in medium difficulty.
The Infernal Way (200 points): Complete game in hard difficulty.
Infernal Power (10 points): Obtain Infernal power.
Teleportation (10 points): Obtain Teleportation power.
Multiple Teleportation (10 points): Obtain multiple Teleportation power.
Mana Booster (30 points): Find 3 mana boosters to increase your mana.
Health Booster (30 points): Find 3 health boosters to increase your health.
Betrayal (20 points): Complete Prologue.
The Dark Angel (20 points): Join the Abyss.
The Cloister (20 points): Get inside the cloister.
Cable Ride (20 points): Get to the upper cloister.
The Acolytes (20 points): Survive the upper cloister.
Walls of Pain (20 points): Complete mission 1.
The Chase (20 points): Find Elena.
Duel (20 points): Defeat Elena.
Going Down (20 points): Find Wolf's lab.
Heaven's Triumph (20 points): Complete mission 2.
Steelworks (20 points): Enter the Steelworks.
Running Man (20 points): Complete mission 3.
Wings of Steel (20 points): Find the plane.
Reflection (20 points): Find the device in the plane.
The Resurrection (20 points): Find Barbara.
Airstrike (20 points): Complete mission 4.
The Island (20 points): Find the Observatory.
The Saint (20 points): Complete Mission 5.
The Cowboy Way (20 points): Find Dual Pistol.
Fire Away (20 points): Fire rocket launcher 20 times.
The Dark Force (20 points): Use infernal powers 100 times.
Precision (20 points): Don't activate the gas traps in the plane.
The Collector (20 points): Retrieve energy from 100 enemies.