Full list of all 47 Halo 3: ODST achievements worth 1,000 gamerscore. It takes around 25-30 hours to unlock all of the achievements on Xbox 360.
Got 10 Rocket kills on Kizingo Boulevard.
Completed the Campaign on Heroic difficulty.
Found all Audio Logs, alone or with another ODST.
Killed 10 Engineers in the city at night, alone or with another ODST.
Got 10 Needler supercombine kills on any covenant.
Killed all Wraiths in Uplift Reserve.
Finished any level with at least one Skull activated.
Completed the Campaign on Normal difficulty.
Completed Coastal Highway and unlocked the Last Exit Firefight mission.
Completed Data Hive and unlocked the Chasm Ten Firefight mission.
Killed 10 enemies with the Flamethrower on Data Hive.
Completed Kikowani Station on Normal, Heroic, or Legendary.
Found the final clue unraveling the mystery, alone or with another ODST.
Completed NMPD HQ and unlocked the Romeo character in Firefight.
Got 15 headshot kills on NMPD HQ.
Completed Kizingo Blvd. and unlocked the Mickey character in Firefight.
Found 15 Audio Logs, alone or with another ODST.
Completed ONI Alpha Site and unlocked the Alpha Site Firefight mission.
Traded weapons with a fellow character.
Got 10 Spartan Laser kills on ONI Alpha Site.
Found the 3rd clue unraveling the mystery, alone or with another ODST.
Got 5 sticky grenade kills in any level.
Found 3 Audio Logs, alone or with another ODST.
Completed Uplift Reserve and unlocked the Dutch character in Firefight.
Found the first Audio Log.
Completed Tayari Plaza and unlocked the Buck character in Firefight.
Found the first clue unraveling the mystery.
Got 10 automag headshot kills in any level.
Accessed and downloaded the city map to your VISR.
Killed 5 enemies while using VISR mode.
Found the first Medical Kiosk and healed yourself.
Stun a vehicle with an overcharged plasma pistol and quickly kill the driver.
Plasma Pistol Overcharge and quickly kill 10 Brutes.
Complete the Campaign on Legendary to unlock a new Firefight character.
Killing things that are new and different is bad, alone or with another ODST.
In Firefight, finish a full round without killing a single enemy.
Score over 200,000 points in Firefight on Crater.
Score over 200,000 points in Firefight on Lost Platoon.
Score over 200,000 points in Firefight on Rally Point.
Score over 200,000 points in Firefight on Security Zone.
Score over 200,000 points in Firefight on Alpha Site.
Score over 200,000 points in Firefight on Windward.
Score over 200,000 points in Firefight on Chasm Ten.
Score over 200,000 points in Firefight on Last Exit.
Finish any level solo on Legendary, on LIVE, with no shots fired or grenades thrown.
In Firefight, on any mission, pass the 4th Set on 4-player Heroic LIVE co-op.
Complete Highway on 4-player Legendary LIVE co-op, with Iron, and no 'Hog or Scorpion.