Full list of all 72 Fallout 3 achievements worth 1,550 gamerscore. It takes around 60-80 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 5 DLC packs containing 22 achievements worth 550 Gamerscore.
Kill all the Super Mutant Behemoths
Discovered 100 locations
Completed "The Superhuman Gambit"
Completed "Those!"
Completed "Head of State"
Completed "Agatha's Song"
Reached Level 20 with Good Karma
Killed 300 people
Completed "Reilly's Rangers"
Completed "Stealing Independence"
Collected 10 Vault-Tec Bobbleheads
Completed "You Gotta Shoot 'Em in the Head"
Completed "Oasis"
Completed "The Replicated Man"
Completed "Blood Ties"
Killed 300 creatures
Completed "The Wasteland Survival Guide"
Placed a grenade or mine while pickpocketing
Completed "Take it Back!"
Completed "The American Dream"
Completed "Finding the Garden of Eden"
Reached Level 14 with Bad Karma
Completed "Picking up the Trail"
Completed "Rescue from Paradise"
Completed "Strictly Business"
Completed "Trouble on the Homefront"
Completed "Big Trouble in Big Town"
Completed "The Waters of Life"
Reached Level 8 with Neutral Karma
Completed "The Power of the Atom"
Completed "Tranquility Lane"
Completed "Scientific Pursuits"
Completed "Galaxy News Radio"
Completed "Following in His Footsteps"
Completed "Escape!"
Took the G.O.A.T.
Got the Pip-Boy 3000
Completed "The Nuka-Cola Challenge"
Completed "Tenpenny Tower"
Reached Level 8 with Bad Karma
Reached Level 8 with Good Karma
Reached Level 14 with Neutral Karma
Reached Level 14 with Good Karma
Reached Level 20 with Bad Karma
Reached Level 20 with Neutral Karma
Made one of every custom weapon
Won 50 Speech Challenges
Hacked 50 terminals
Picked 50 locks
Collected 20 Vault-Tec Bobbleheads
Completed "Aiding the Outcasts"
Completed "Paving the Way"
Completed "Operation: Anchorage"
Completed "The Guns of Anchorage"
Completed "Free Labor"
Found All 100 Steel Ingots
Completed "Unsafe Working Conditions"
Completed "Into The Pitt"
Reached Level 30 with Bad Karma
Reached Level 30 with Neutral Karma
Reached Level 30 with Good Karma
Completed "Who Dares Wins"
Completed "Shock Value"
Completed "Death From Above"
Completed "A Meeting of the Minds"
Completed "Walking With Spirits"
Completed "The Local Flavor"
Discovered all locations within Point Lookout
Completed "This Galaxy Ain't Big Enough…"
Completed "Among the Stars"
Completed "Not of This World"
Collected all Alien Captive Recordings