Full list of all 58 Halo Wars achievements worth 1,200 gamerscore. It takes around 80-100 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 50 achievements worth 1,000 Gamerscore, and there are 2 DLC packs containing 8 achievements worth 200 Gamerscore.
100% Completion
Got 20,000 points in any Skirmish Game
Mission 7: Did not destroy any Power Node
Mission 6: Successfully protected every Rhino
Mission 1: Rammed 50 Grunts with Warthogs
Got a Gold Medal on every Campaign Mission
Completed entire Campaign in Co-op Mode
Finished all missions under Par Time on Heroic difficulty
Won a Skirmish Game with Dual Scarabs
Got a winning High Score with 10 or less Squads against the Heroic AI
Won a Heroic Skirmish Game against the AI in under 10 minutes
Won a game on every Skirmish Map
Won a Skirmish Game with every Leader
Unlocked All Timeline Events
Got a Gold Medal with all Debuff Skulls Active
Completed the Campaign on Heroic Difficulty
Completed the Campaign on Legendary Difficulty
Collected all Skulls
Mission 14: Didn't claim an extra base
Mission 13: Destroyed 25 units with the Scarab
Mission 12: Repaired the Power Core in less than 4 minutes
Mission 11: Saved all the Airlocks
Obtained a Lifetime Campaign Score over 1,000,000
Mission 8: Used Elephants to train 100 Infantry
Mission 5: Jacked 6 Covenant Vehicles
Mission 4: Saved Adam
Obtained the Lieutenant Rank on Xbox LIVE
Unlocked 20 Timeline Events
Won a 3v3 Skirmish game with 2 AI Allies
Won a game in every Skirmish Game Mode
Played Halo Wars for at least 24 Total Hours
Used one of the 6 Major Leader Powers to destroy an enemy's last unit
Mission 3: Killed at least 5 Covenant Units with the Bridge
Improved your Score in any Campaign Mission
Completed any Campaign Mission in Co-op Mode
Mission 2: Destroyed every Methane Tank
Won and had the Highest Score in a Matchmade Skirmish Game on Xbox LIVE
Obtained the Recruit Rank on Xbox LIVE
Won a Matchmade Skirmish Game on Xbox LIVE
Completed Act IV on any difficulty
Mission 15: Opened the Doors in order
Got a Gold Medal on any mission
Completed Act III on any difficulty
Mission 10: Disrupted all Tractor Beams
Mission 9: Put every Colony in Hibernation Mode at the same time
Completed Act II on any difficulty
Completed Act I on any difficulty
Collected your first Skull
Completed Mission 1 on any difficulty
Obtain the General Rank on Xbox LIVE
Scored the winning point in a game of Keepaway against Legendary AIs.
Won and never trailed in a Tug of War game.
Got a Scarab during a Reinforcement game.
Gained at least 15 population from a single wave in a Reinforcement game.
Hot drop 50 squads to your Covenant Leader in a single game on Barrens.
Finish with 5000 net resources tributed to your teammates on Memorial Basin except in Deathmatch.
Kill 20 enemy squads with a continuous Covenant Leader Power on Memorial Basin.
Disrupt 5 active Leader Powers in a single game on Blood River.