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

Epic Saga (50 points): Complete Story Mode on Hard.
Scrap Metal (20 points): Destroy 27 Stalkers.
Decked Out (35 points): Win 10 ranked matches fully equipped.
Totaled Eclipse (25 points): Destroy 9 Eclipses.
Veteran's Affair (40 points): Win 99 ranked matches.
Eradicator (30 points): Beat the AI on all Skirmish maps.
Epic Campaign (30 points): Complete Story Mode on Easy or Normal.
The Other Side (25 points): Complete Act 1 of Story Mode.
The Other Path (25 points): Complete Act 2 of Story Mode.
Qualify for Duty (15 points): Complete the Tutorial.
Clean Sweep (10 points): Destroy all hiding Sai insurgents in the Tutorial.
Ulterior Motives (10 points): Use the playbook to switch weapons.
First Assault (20 points): Complete Mission 1: Domestic Disturbance.
In Transit (20 points): Secure the Control Node powering the turrets in Mission 2: Assault Charge.
Telepathic (20 points): Establish a portal in Mission 3: Double Jeopardy.
H.Y.D.R.A. (20 points): Defeat the Hydra in Mission 4: Multiple Counts.
Hammer Time (20 points): Take out the Arc-Hammers in Mission 5: Self Defense.
Evacuation (20 points): Rescue Vantage in Mission 6: Innocent Victim.
A Bridge Not Too Far (20 points): Secure all 3 bridges in Mission 7: Unfair Surprise.
Power Up (20 points): Secure all 3 power junctions in Mission 8: Reasonable Doubt.
Fur Coat (20 points): Defeat Sable in Mission 9: Shock Verdict.
Rite of Passage (25 points): Rescue Eona in Mission 10: Prison Break.
In Pursuit (25 points): Secure the AA Turrets in Mission 11: Hot Pursuit.
Reverse Polarity (25 points): Recalibrate the airfield station in Mission 12: Natural Justice.
Spray and Pray (15 points): Use the Matriarch's Acid Rain ability.
Demolisher (25 points): Destroy 55 Control Nodes with the Demo Bomb ability.
Puppet Master (20 points): Destroy an enemy unit with one you have Mind-Controlled.
Unleashed (15 points): Use the Rage Smash ability.
Playing Both Sides (15 points): Win 8 ranked matches with each faction.
Demoraliser (20 points): Destroy 11 enemy units in the first 5 minutes of a ranked match.
First Down and Ten (20 points): Win a ranked match in under 10 minutes.
Winning Streak (25 points): Win 6 consecutive ranked matches.
Feeding the Habit (15 points): Play 16 ranked matches.
Calling all Units (15 points): Recruit one of every unit type in any game mode.
Gone Shopping (20 points): Lose a multiplayer match while the deployment queue is open.
Maximum Firepower (20 points): Upgrade a Control Node to have level 3 turrets (multiplayer or skirmish).
Slice and Dice (15 points): Use the Spectre's Rapid Slice ability to kill an enemy commander (multiplayer or skirmish).
False Sense of Security (25 points): Attack 24 cloaked Spectres while using the Infiltrator's Thermal Vision.
Appetite for Destruction (25 points): Destroy 77 units using the Stalker's SAMs.
Pest Control (20 points): Kill 80 Broodlings.

Additionally, there are three secret achievements:

Full Repertoire (50 points): Use all unit abilities at least once.
Formidable (50 points): Destroy 500 units.
Whip it Good (20 points): Whip 250 times during any map or match.