Full list of all 49 Mass Effect achievements worth 1,200 gamerscore. It takes around 60-80 hours to unlock all of the achievements in the base game on Xbox 360.
The base game contains 45 achievements worth 1,000 Gamerscore, and there are 2 DLC packs containing 4 achievements worth 200 Gamerscore.
Complete Feros
Complete Eden Prime
150 Pistol Kills
Land on an uncharted world
Player is Spectre
Complete Mass Effect Playthrough
Complete Virmire
Complete Noveria
Complete 2 Playthroughs
Complete Hardcore Playthrough
150 Shotgun Kills
150 Assault Rifle Kills
Complete playthrough with shield damage greater than health damage
Exceed 1,000,000 Credits
150 organic enemy kills
250 synthetic enemy kills
75% of total Renegade points
75% of total Paragon points
Complete romance subplot
Resolved impossible situation with Charm or Intimidate
Found Liara in Artemis Tau Cluster
150 Sniper Rifle Kills
50th level character
Complete the majority of the game with the krogan squad member
Complete the majority of the game with the Alliance soldier squad member
Complete the majority of the game with the Alliance sentinel squad member
Use AI Hacking 75 times
Use biotic Singularity 75 times
Use biotic Warp 75 times
Use Neural Shock 75 times
Complete the majority of the game with the turian squad member
Use biotic Stasis 75 times
Use biotic Lift 75 times
Use biotic Throw 75 times
Use Damping Field 75 times
Use Shield Overload 75 times
Complete Insanity Playthrough
Find all primary Alien: Council Races, Extinct Races and Non-Council Races codex entries
60th level character
Complete the majority of the game with the asari squad member
Complete the majority of the game
Complete the majority of the game with the quarian squad member
Use biotic Barrier 75 times
Use medi-gel 150 times
Use Sabotage 75 times
You completed the Bring Down the Sky mission.
You completed Ahern's survival mission
Took first place in 12 combat scenarios on Pinnacle Station
Took first place in a combat scenario on Pinnacle Station