Full list of all 79 Gears of War 2 achievements worth 1,750 gamerscore. It takes around 80-100 hours to unlock all of the achievements in the base game.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 5 DLC packs containing 29 achievements worth 750 Gamerscore.
Completed all campaign acts on Normal Difficulty
Completed all campaign acts on Hardcore Difficulty
Completed all campaign acts on Insane Difficulty
Recovered 20 of 41 collectibles
Played 1999 rounds in multiplayer
Used 10 meatshields to survive
Won 3 matches of Wingman (not Custom)
Completed all acts in Co-op on any difficulty
Defeated the Lambent Brumak
Completed all campaign acts on Casual Difficulty
Captured a Brumak
Successfully defended COG headquarters
Defeated Skorge and his Hydra
Found the Locust queen
Won 3 matches of King of the Hill (not Custom)
Got up close and personal with the Boomshield
Activated Jack as homing beacon in Nexus
Found Maria
Executioner with style
Defeated the Leviathan
Arrived safely at Mount Kadar Stranded camp
Killed 10 enemies with a grenade while down but not out
Discovered the location of the Locust queen
Performed a chainsaw multiple bypass
Completed 10 chapters in Co-op on any difficulty
Freed Baird from capture
Watched Ilima sink
Seen the sights with Betty
Recovered 5 of 41 collectibles
Bashed 30 Tickers
Completed 1 chapter in Co-op on any difficulty
Won a match on every map shipped with the game
Won all Training Grounds matches
Torched 30 enemies
Team survived 10 Horde waves
Killed 30 enemies with your Mulcher turret
Killed 30 enemies raining down death from the sky
Submitted a spectator photo
Won 10 rounds of Guardian as the leader (not Custom)
Killed an enemy with every weapon
Won 10 chainsaw duels
Effectively used grenade mines
Escorted Betty to Landown
Successfully defended the hospital
Showed Carmine the ropes
Mastered the ways of the Active Reload
Recover all 41 collectibles (any difficulty)
Kill 100,000 enemies (any mode)
Capture 10 meatflags in Submission (not Custom)
Survive all 50 waves of Horde (any difficulty, any map)
Won a Wingman match on each of the Flashback Map Pack maps
Won a match on each of the Flashback Map Pack maps
Complete waves 1 through 10 on all Flashback Map Pack maps in Horde (any difficulty)
Won a Wingman match on each of the Combustible Map Pack maps
Won a match on each of the Combustible Map Pack maps
Survive first 10 Horde waves on Combustible Map Pack maps as a team
Win an Annex match on each Flashback and Combustible Map Pack map (not Custom)
Reached level 25 in multiplayer
Reached level 15 in multiplayer
Reached level 5 in multiplayer
Became an ultimate Gearhead at level 100
Reached level 50 and played in the snow
Played in the snow and won on all of the Snowblind Map Pack maps
Played in the snow on all of the Snowblind Map Pack maps
Complete waves 1 through 10 on all Snowblind Map Pack maps in Horde (any difficulty)
Complete waves 1 through 50 on any Snowblind Map Pack map in Horde (any difficulty)
Reached level 15 and found some Horde Sanctuary
Reached level 30 and paid your Horde respects
Reached level 20 and stopped at the Horde Way Station
Made it through "Road to Ruin" with nothing but vengeance on your mind
Played a match on all of the Dark Corners Map Pack maps
Won a match on all of the Dark Corners Map Pack maps
Reached level 10 and hit the Horde Highway
Cooked up some Bloodmount BBQ with 25 roastings
Made it through "Road to Ruin" with a friend
Made it through "Road to Ruin" dressed as a Theron Guard
Reached level 8 and rocked Horde old school
Reach level 40 in multiplayer and complete waves 1 - 40 on the Memorial map in Horde
Reach level 50 in multiplayer and complete waves 1 - 50 on the Nowhere map in Horde