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