Here is the full list of all 56 Gears of War: Ultimate Edition achievements worth 1,250 gamerscore.
Won 25 matches in Boxes
Reached Level 100 and re-upped
Completed 100 matches in ring-based game types and captured 3 objectives in each match
Killed 3 enemies at once 10 different times
Revived 100 teammates in Versus multiplayer
Spotted 100 enemies ending in an assisted kill in Versus
Defeated General RAAM in co-op on Insane without either player being DBNO
Defeated General RAAM
Completed all acts on Casual Difficulty
Completed all acts on Normal Difficulty
Completed all acts on Hardcore Difficulty
Completed all acts on Insane Difficulty
Completed all acts in co-op
Recovered all 33 COG tags
Boarded the Imulsion bound train with the Lightmass Bomb
Killed the Brumak
Restored communications with Control
Restored power to the bridge
Escaped from the Brumak (end of Ch.6)
Discovered Adam's secret lab
Killed a Berserker in the Conservatory
Delta found downed chopper
Deployed the Sonic Resonator
Killed a Corpser
Recovered 22 COG tags
Delta descended into the mines
Reunited with Baird and Cole inside the Imulsion Factory
Won a match on every Versus map
Reached level 25
Won a match in every Versus game type
Won 25 matches in Team Deathmatch
Killed an enemy with every weapon in Versus
Reached level 10
Won 10 Versus matches without losing a round
Read one full comic
Reached level 5
Finished with the highest points in a Versus match
Defended Stranded Settlement and headed to Lethia Imulsion Factory
Got the Junker at Chap's gas station
Used the spotlight as protection from the Kryll
Made a Deal with Franklin
Completed 10 different chapters in co-op
Closed all 4 e-holes around the fountain in Fish in a Barrel without any Locust fully emerging
Completed 1 co-op chapter in co-op
Killed the Berserker in the Tomb of the Unknown
Recovered 11 COG tags
Rescued Damon Baird from the Tomb of the Unknown
Rescued Augustus Cole in the House of Sovereigns
Performed 25 perfect active reloads
Escaped from the Slab
Completed tutorial path on any difficulty
Performed 5 perfect active reloads in a row
Finished playing a Versus match
Played one Versus Match with a Custom Weapon Skin
Kill 10,000 people in Versus matches
Win 20 rounds in ring-based game types on Xbox Live by shutting out the opposing team