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

I'm Supposed To Die Tonight (20 points): Complete Mission 1 on any difficulty.
Get In My Car (20 points): Complete Mission 2 on any difficulty.
Candy Shop (20 points): Complete Mission 3 on any difficulty.
Straight To The Bank (20 points): Complete Mission 4 on any difficulty.
Disco Inferno (20 points): Complete Mission 5 on any difficulty.
Amusement Park (20 points): Complete Mission 6 on any difficulty.
Gunz Come Out (20 points): Complete Mission 7 on any difficulty.
I'll Still Kill (20 points): Complete Mission 8 on any difficulty.
Gotta Make It To Heaven (20 points): Complete Mission 9 on any difficulty.
Got Paid (25 points): Complete all missions on Easy or better difficulty level.
Gangsta (50 points): Complete all missions on Normal or better difficulty level.
Bulletproof (100 points): Complete all missions on Hard difficulty level.
Packin' Heat (10 points): Unlock all pistols.
Point Blank (10 points): Unlock all close combat weapons.
Rifled (10 points): Unlock all assault weapons.
Explosive (10 points): Unlock all special weapons.
Tooled Up (50 points): Unlock all weapons.
Wanna-be (10 points): Obtain 15 or more Silver Badges.
Regular (25 points): Obtain all Silver Badges.
Hardcore (50 points): Obtain 15 or more Gold Badges.
O.G. (100 points): Obtain all Gold Badges.
Savior (5 points): Revive a coop player.
We're Supposed To Die Tonight (10 points): Complete Mission 1 on any difficulty as a member of G-Unit.
Get In Our Car (10 points): Complete Mission 2 on any difficulty as a member of G-Unit.
Our Candy Shop (10 points): Complete Mission 3 on any difficulty as a member of G-Unit.
We're Going Straight To The Bank (10 points): Complete Mission 4 on any difficulty as a member of G-Unit.
Our Disco Inferno (10 points): Complete Mission 5 on any difficulty as a member of G-Unit.
Our Amusement Park (10 points): Complete Mission 6 on any difficulty as a member of G-Unit.
Our Gunz Come Out (10 points): Complete Mission 7 on any difficulty as a member of G-Unit.
We'll Still Kill (10 points): Complete Mission 8 on any difficulty as a member of G-Unit.
We Gotta Make It To Heaven (10 points): Complete Mission 9 on any difficulty as a member of G-Unit.
G-Unit (50 points): Complete all missions on any difficulty as a member of G-Unit.
Hit and Run (10 points): Run over a foot soldier in a driving section.
Ramping Up (10 points): Complete any of the ramp scenarios in a driving section.
Death From Above (10 points): Destroy 50 vehicles and destroyable objects on the flying level without dying.
Up Close (5 points): Perform a counter kill.
Got It Done (5 points): Successfully complete one scenario.
Scenario Master (20 points): Successfully complete 50 scenarios.
Black Belt (40 points): Unlock all counter kill packs.
Sharpshooter (25 points): Kill an enemy by shooting a rocket or grenade out of the air using Gangsta Fire.
Fly Poster (15 points): Collect all 5 posters on any level. This can also be achieved by assisting another player in Coop.
Target Practice (15 points): Shoot all 5 targets on any level. This can also be achieved by assisting another player in Coop.
Flying High (10 points): Score air time from a single character for more than 10 seconds.
Massacre (10 points): Kill 5 enemies fast enough to score a 5 kill combo.
Millionaire (50 points): Have 1,000,000 dollars in the bank.

Additionally, there is one secret achievement:

Not Bulletproof (0 points): Died on Easy difficulty.