Here is the full list of all 56 Gears of War: Ultimate Edition achievements worth 1,250 gamerscore.
Killed 3 enemies at once 10 different times
Recovered all 33 COG tags
Completed all acts on Insane Difficulty
Defeated General RAAM in co-op on Insane without either player being DBNO
Read one full comic
Closed all 4 e-holes around the fountain in Fish in a Barrel without any Locust fully emerging
Defeated General RAAM
Completed all acts on Casual Difficulty
Completed all acts on Normal Difficulty
Completed all acts on Hardcore Difficulty
Completed all acts in co-op
Recovered 22 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
Reached level 5
Killed a Berserker in the Conservatory
Delta found downed chopper
Deployed the Sonic Resonator
Killed a Corpser
Delta descended into the mines
Reunited with Baird and Cole inside the Imulsion Factory
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
Recovered 11 COG tags
Made a Deal with Franklin
Completed 10 different chapters in co-op
Killed the Berserker in the Tomb of the Unknown
Rescued Damon Baird from the Tomb of the Unknown
Rescued Augustus Cole in the House of Sovereigns
Performed 25 perfect active reloads
Completed 1 co-op chapter in co-op
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
Spot 100 enemies ending in a kill in Versus (social or competitive)
Revive 100 teammates in Versus multiplayer (social or competitive)
Finish with the highest point in a Versus match (social or competitive)
Win a match in every Versus game type (social or competitive)
Win a match in every Versus map (social or competitive)
Win 10 Versus matches without losing a round (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 10
Reach level 25
Reach level 100 and re-up
Kill an enemy with every weapon in Versus (social or competitive)
Win 25 matches in Team Deathmatch