Complete each achievement to get the allotted gamerscore.
Unlockable How to Unlock
Blood Trial (5) Complete "Blood Trial" challenge
Close Up (5) Complete "Close Up" challenge
Leap Up! (5) Complete "Leap Up!" challenge
Kaboom (5) Complete "Kaboom" challenge
Train Wreck (5) Complete "Train Wreck" challenge
Swinger (5) Complete "Swinger" challenge
Man Locked Up (5) Complete "Man Locked Up" challenge
Stroke of Luck (5) Complete "Stroke of Luck" challenge
Kick In The Back (10) Complete "Kick In The Back" challenge
Receiving End (10) Complete "Receiving End" challenge
Jabber Man (10) Complete "Jabber Man" challenge
Incoming! (10) Complete "Incoming!" challenge
Slayer (10) Complete "Slayer" challenge
Torn Into Pieces (10) Complete "Torn Into Pieces" challenge
Fair Fight! (10) Complete "Fair Fight!" challenge
Cracker (15) Complete "Cracker" challenge
Whoo-paah! (10) Complete "Whoo-paah!" challenge
Down To Earth (10) Complete "Down To Earth" challenge
Rocket Man (10) Complete "Rocket Man" challenge
Two Hit Wonder (10) Complete "Two Hit Wonder" challenge
Explosive Delivery (10) Complete "Explosive Delivery" challenge
The Pinball Effect (10) Complete "The Pinball Effect" challenge
Worthy Foe (10) Complete "Worthy Foe" challenge
Spence is in the Air (10) Complete "Spence is in the Air" challenge
The River (10) Complete "The River" challenge
Let the Dog Out (15) Complete "Let the Dog Out" challenge
Barrage (15) Complete "Barrage" challenge
Air to Surface (20) Complete "Air to Surface" challenge
Drive-by (20) Complete "Drive-by" challenge
Pull! (15) Complete "Pull!" challenge
Come Out and Play (20) Complete "Come Out and Play" challenge
Crowd Control (20) Complete "Crowd Control" challenge
Shoot 'Em Up! (15) Complete "Shoot 'Em Up!" challenge
Out of the Bush (30) Complete "Out of the Bush" challenge
Can you dig it? (40) Complete "Can you dig it?" challenge
Feel the Beat, Y'all! (25) Complete "Feel the Beat, Y'all!" challenge
Shellshock (25) Complete "Shellshock" challenge
Headshot Bonanza (25) Complete "Headshot Bonanza" challenge
Poly Cruncher (25) Complete "Poly Cruncher" challenge
Nemesis (25) Complete "Nemesis" challenge
Biomech Sweeper (25) Complete "Biomech Sweeper" challenge
Whip 'Em Good (25) Complete "Whip 'Em Good" challenge
I got Hard (75) Finish the game in Hard mode.
The Pitcher (25) Complete "The Pitcher" challenge
The Collector (50) Find all collectibles in the game.
I went Commando (100) Finish the game in Commando mode.
Bionically Challenged (50) Complete all challenges in the game.
End Game (50) Complete the final mission
Choke on that (50) Kill Groeder - Kill him for good
Challenges

Challenges are optional task that are seperate from the main objective. They become available as you progress through the game, and by completing them you unlock more challenges, new moves and upgrades. They can be viewed at any time once available via the info screen.
Unlockable How to Unlock
Weapon Usage: Close up Shoot an enemy while zoomed in to complete the challenge.
Weapon Usage: Two Hit Wonder Kill 2 guards with a single hiker shot to complete the challenge.
Weapon Usage: Kaboom Use a grenade to kill a grunt to complete the challenge.
Arm and Wire Action: Train Block Pull down the vehicle that is blocking your way to complete the challenge.
Arm and Wire Action: Train Wreck Pull down 3 train cars to complete the challenge.
Arm and Wire Action: Swinger Complete 3 consecutive swings to complete the challenge.
Arm and Wire Action: Speed Swinger Complete 5 consecutive speed swings to complete the challenge.
Arm and Wire Action: Leap Up! Perform a leap up to complete the challenge.
Arm and Wire Action: Kick In The Back Perform 2 zip kicks on an enemy to complete the challenge.
Arm and Wire Action: First Swing Perform a swing to complete the challenge.
Arm and Wire Action: Hand-To-Hand Kill a grunt in hand-to-hand combat to complete the challenge.
Arm and Wire Action: Reel In Reel in 3 times to complete the challenge.
Enemy Combat: Slayer Kill 25 enemy grunts to complete the challenge.
Enemy Combat: Blood Trial Kill 10 grunts to complete the challenge.
Enemy Combat: Headshot Bonanza Kill 50 grunts with a headshot to complete the challenge.