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