Here is the full list of all 41 Dark Souls (GFWL) achievements worth 1,000 gamerscore. It takes around 60-80 hours to unlock all of the achievements.
All achievements completed. Congratulations!
Acquire all sorceries.
Acquire all rare weapons.
Acquire all pyromancies.
Acquire all miracles.
Acquire best weapon through magic reinforcement.
Acquire best weapon through crystal reinforcement.
Acquire best weapon through raw reinforcement.
Acquire best weapon through chaos reinforcement.
Acquire best weapon through fire reinforcement.
Discover Gravelord Servant covenant.
Reach "The Dark Lord" ending.
Acquire best weapon through lightning reinforcement.
Acquire best weapon through enchanted reinforcement.
Acquire best weapon through divine reinforcement.
Discover Darkwraith covenant.
Discover Forest Hunter covenant.
Discover Way of White covenant.
Reach "To Link the Fire" ending.
Acquire best weapon through occult reinforcement.
Defeat the Soul Lord Bed of Chaos.
Discover Path of the Dragon covenant.
Defeat Dark Sun Gwyndolin, the Darkmoon God.
Defeat Seath the Scaleless, inheritors of souls.
Defeat the Four Kings, inheritors of souls.
Acquire best weapon through standard reinforcement.
Acquire the Art of Abysswalking.
Discover Blade of the Darkmoon covenant.
Defeat the Soul Lord Gravelord Nito.
Acquire the Rite of Kindling.
Discover Princess's Guard covenant.
Acquire the Lordvessel.
Defeat Crossbreed Priscilla, the Lifehunter.
Discover Chaos Servant covenant.
Arrive in Anor Londo.
Ring Bell of Awakening in Quelaag's domain.
Discover Warrior of Sunlight covenant.
Ring Bell of Awakening at Undead Church.
Arrive in Lordran.
Acquire Estus Flask.
Light bonfire flame.