Full list of all 57 Gears of War achievements worth 1,250 gamerscore. It takes around 150-200 hours to unlock all of the achievements in the base game.
The base game contains 49 achievements worth 1,000 Gamerscore, and there are 2 DLC packs containing 8 achievements worth 250 Gamerscore.
Kill 10,000 people in versus ranked match total
Kill 100 enemies in ranked matches with an execution
Kill 100 enemies in ranked matches with grenade tag
Kill 100 enemies in ranked matches with the curb stomp
Kill 100 enemies in ranked matches with a pistol
Kill 100 enemies in ranked matches with the Longshot
Kill 100 enemies in ranked matches with the Torque Bow
Kill 100 enemies in ranked matches with a headshot
Kill 100 enemies in ranked matches with the Boomshot
Revive 100 teammates in ranked matches
Kill 100 enemies in ranked matches with the Chainsaw
Kill 100 enemies in ranked matches with the Hammer of Dawn
Win 10 ranked matches without losing a round
Complete Act 3 on Hardcore Difficulty
Complete Act 3 on Insane Difficulty
Defeat a Corpser on Hardcore Difficulty
Host and complete 50 ranked matches
Win a ranked match on every versus map
Win a ranked match in every versus game type
Kill 3 enemies at once 10 different times (on any difficulty)
Complete all acts in co-op as Dominic Santiago on any difficulty
Complete all acts on Hardcore Difficulty
Complete Act 5 on Hardcore Difficulty
Complete all acts on Insane Difficulty
Complete Act 5 on Insane Difficulty
Defeat General RAAM on Hardcore Difficulty
Complete Act 4 on Hardcore Difficulty
Complete Act 4 on Insane Difficulty
Complete Act 2 on Hardcore Difficulty
Complete Act 2 on Insane Difficulty
Complete 10 different co-op chapters as Dominic Santiago on any difficulty
Complete Act 1 on Hardcore Difficulty
Complete Act 1 on Insane Difficulty
Defeat a Berserker on Hardcore Difficulty
Complete 1 co-op chapter as Dominic Santiago on any difficulty
Complete all acts on Casual Difficulty
Complete Act 5 on Casual Difficulty
Recover all of the COG tags (on any difficulty)
Complete Act 4 on Casual Difficulty
Complete Act 3 on Casual Difficulty
Recover two-thirds of the COG tags (on any difficulty)
Complete Act 2 on Casual Difficulty
Complete Act 1 on Casual Difficulty
Recover one-third of the COG tags (on any difficulty)
Completed tutorial level on any skill level
Finish with the highest points in a ranked match
Finish playing a versus ranked match
Perform 25 perfect active reloads (on any difficulty)
Perform 5 perfect active reloads in a row (on any difficulty)
Win 20 multiplayer matches of 3+ rounds in any game type on the Subway multiplayer map
Win 20 multiplayer matches of 3+ rounds in any game type on the Garden multiplayer map
Win 20 multiplayer matches of 3+ rounds in any game type on the Bullet Marsh multiplayer map
Win 20 multiplayer matches of 3+ rounds in any game type on the Process multiplayer map
Win a multiplayer match of 3+ rounds in any game type on 6 different downloadable maps
Complete 100 multiplayer matches of 3+ rounds in Annex and capture 3 objectives in each match
Win 20 rounds of multiplayer matches in Annex by shutting out the opposing team
Win 20 rounds of multiplayer matches in Annex by fewer than 5 points