Complete the following achievements to unlock Xbox Live Gamerscore points.

Zombie Slaughter (20 points): Kill 500 zombies.
Zombie Destruction (20 points): Kill 5,000 zombies.
Z-Genocider 2: Genocide Harder (20 points): Kill 53,596 zombies.
Zombie Genocide Master (20 points): Kill 72,000 zombies.
Vigilante Justice (20 points): Defeat 5 psychopaths.
Judge, Hury and Executioner (20 points): Defeat 10 psychopaths.
Zombie Fu (20 points): Kill 1,000 zombies barehanded.
Wrong kind of "Chopper" (20 points): Kill 1,000 zombies while riding a motorcycle.
He hasn't covered wars... (20 points): Use every type of firearm on a zombie.
Head Trauma (20 points): Use every type of melee weapon on a zombie.
Death From Afar (20 points): Use every type of ranged weapon on a zombie.
Explosive Temper (20 points): Use every type of explosive on a zombie.
Slaughter - S = Laughter! (20 points): Use every type of novelty weapon on a zombie.
Come on! Follow me! (20 points): Escort 8 survivors at once.
Saving the Day (20 points): Save 10 survivors.
Hero of Fortune City (20 points): Save 50 survivors.
Needs more chainsaw (20 points): Create a combo weapon.
Duct Tape FTW (20 points): Create all combo weapons.
Apprentice Rising (20 points): Reach level 25.
Professional Rising (20 points): Reach level 50.
Fashion Aficionado (20 points): Change into 10 different pieces of clothing.
Chuck Greene: Crosso Dresser? (20 points): Change into all the clothes in the game.
Clean Record (20 points): Complete The Facts.
Bartender (20 points): Mix a drink.
Look at all that juice! (20 points): Create and consume all mixed drinks in the game.
Finally Full (20 points): Eat all types of food in the game.
Having A Gas (20 points): Kill 1,000 "special" zombies.
Father of the Month (20 points): Give Katey a gift.
Father of the Year (20 points): Give Katey every possible gift.
Justice Served (20 points): Complete Overtime Mode.
Better With a Friend (20 points): Solve all case files in Co-op.
Don't you die on me! (20 points): Revive another player in Co-op.
Big Spender (20 points): Spend $6,000,000 in Fortune City.
Window Shopper (20 points): Enter all the stores in the game.
Masquerade (20 points): Have 10 zombies with masks on at once.
Improper Behavior (20 points): Spraypaint all Zombrex posters.
TK's Favorite (20 points): Play and win in all 9 TIR events.
Rising Star (20 points): Come in first place in a single TIR event.
Win Big! (20 points): Finish in first place in a TIR episode.
Custom Finish (20 points): Give your bike a custom paint job.
Curiously Inventive (20 points): Collect all combo cards hidden in Fortune City.
Life Saver (20 points): Collect all survivor combo cards.
Tough Guy (20 points): Collect all combo cards from psychopaths.
Half Deck (20 points): Collect 25 combo cards.
Full Deck (20 points): Collect all combo cards.
Data Miner (20 points): Fill all entries in the notebook.
Smashy (20 points): Smash 100 zombies using the Smash skill move.
Stick 'em up (20 points): Stick it to a zombie by covering him in weapons and objects!
The Skill To Survive (20 points): Tame Snowflake.

Additionally there is one secret achievement.

Tape it or DIE! (20 points): Discovered the secret combo card. Did you cheat by checking online?