Here is the full list of all 56 Gears of War: Ultimate Edition achievements worth 1,250 gamerscore.
Completed all acts on Hardcore Difficulty
Completed all acts on Insane Difficulty
Completed all acts in co-op
Completed 10 different chapters in co-op
Killed an enemy with every weapon in Versus
Defeated General RAAM
Completed all acts on Casual Difficulty
Completed all acts on Normal Difficulty
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
Spotted 100 enemies ending in an assisted kill in Versus
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
Reached level 25
Completed 1 co-op chapter in co-op
Won a match on every Versus map
Defended Stranded Settlement and headed to Lethia Imulsion Factory
Got the Junker at Chap's gas station
Won 25 matches in Team Deathmatch
Used the spotlight as protection from the Kryll
Won 10 Versus matches without losing a round
Made a Deal with Franklin
Read one full comic
Killed the Berserker in the Tomb of the Unknown
Recovered 11 COG tags
Reached level 10
Rescued Damon Baird from the Tomb of the Unknown
Rescued Augustus Cole in the House of Sovereigns
Reached level 5
Finished playing a Versus match
Finished with the highest points in a Versus match
Played one Versus Match with a Custom Weapon Skin
Performed 25 perfect active reloads
Performed 5 perfect active reloads in a row
Escaped from the Slab
Completed tutorial path on any difficulty
Kill 3 enemies at once 10 different times (on any difficulty)
Revive 100 teammates in Versus multiplayer (social or competitive)
Win a match in every Versus game type (social or competitive)
Kill 10,000 people in Versus matches
Complete 100 matches in ring-based game types on Xbox Live and capture 3 objectives in each match
Win 20 rounds in ring-based game types on Xbox Live by shutting out the opposing team
Win 25 matches in Boxes (social or competitive)
Reach level 100 and re-up
Defeat General RAAM in co-op on Insane without either player being DBNO
Close all 4 e-holes around the fountain in Fish in a Barrel without any Locust fully emerging