Full list of all 50 Gears of War (GFWL) achievements worth 1,000 gamerscore. It takes around 80-100 hours to unlock all of the achievements.
Complete 1 co-op chapter as Dominic Santiago on any difficulty
Finish playing a versus ranked match
Recover one-third of the COG tags (on any difficulty)
Complete Act 1 on Casual Difficulty
Complete Act 1 on Hardcore Difficulty
Defeat a Berserker on Hardcore Difficulty
Perform 5 perfect active reloads in a row (on any difficulty)
Perform 25 perfect active reloads (on any difficulty)
Complete tutorial level on any skill level
Complete Act 2 on Casual Difficulty
Complete Act 3 on Casual Difficulty
Complete Act 4 on Casual Difficulty
Complete Act 5 on Casual Difficulty
Complete all acts on Casual Difficulty
Complete Act 2 on Hardcore Difficulty
Complete Act 3 on Hardcore Difficulty
Complete Act 4 on Hardcore Difficulty
Complete Act 5 on Hardcore Difficulty
Complete all acts on Hardcore Difficulty
Complete Act 1 on Insane Difficulty
Complete Act 2 on Insane Difficulty
Complete Act 3 on Insane Difficulty
Complete Act 4 on Insane Difficulty
Complete Act 5 on Insane Difficulty
Complete all acts on Insane Difficulty
Recover two-thirds of the COG tags (on any difficulty)
Recover all of the COG tags (on any difficulty)
Defeat a Corpser on Hardcore Difficulty
Defeat General RAAM on Hardcore Difficulty
Kill 3 enemies at once 10 different times (on any difficulty)
Kill 10,000 people in versus player match total
Complete 10 different co-op chapters as Dominic Santiago on any difficulty
Complete all acts in co-op as Dominic Santiago on any difficulty
Revive a teammate in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with the Boomshot in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with a pistol in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with the Torque Bow in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with the Longshot in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with the Hammer of Dawn in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with the Chainsaw in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with a curb stomp in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with an execution in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with a grenade tag in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Kill an enemy with a headshot in 100 multiplayer (Player or Ranked) matches of 3+ rounds
Finish with the highest points in a ranked match
Win a ranked match in every versus game type
Win a ranked match on every versus map
Win 10 ranked matches without losing a round
Kill 10,000 people in versus ranked match total
Defeat a Brumak on Hardcore Difficulty