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 rare weapons.
Reach "To Link the Fire" ending.
Acquire all miracles.
Discover Warrior of Sunlight covenant.
Reach "The Dark Lord" ending.
Discover Forest Hunter covenant.
Defeat Dark Sun Gwyndolin, the Darkmoon God.
Discover Blade of the Darkmoon covenant.
Acquire best weapon through chaos reinforcement.
Acquire best weapon through fire reinforcement.
Acquire best weapon through magic reinforcement.
Acquire best weapon through enchanted reinforcement.
Acquire all sorceries.
Defeat Seath the Scaleless, inheritors of souls.
Acquire best weapon through occult reinforcement.
Discover Path of the Dragon covenant.
Acquire all pyromancies.
Defeat the Soul Lord Bed of Chaos.
Discover Chaos Servant covenant.
Defeat the Soul Lord Gravelord Nito.
Acquire best weapon through divine reinforcement.
Acquire best weapon through crystal reinforcement.
Acquire best weapon through raw reinforcement.
Acquire best weapon through standard reinforcement.
Acquire best weapon through lightning reinforcement.
Defeat Crossbreed Priscilla, the Lifehunter.
Discover Princess's Guard covenant.
Discover Way of White covenant.
Discover Gravelord Servant covenant.
Discover Darkwraith covenant.
Defeat the Four Kings, inheritors of souls.
Acquire the Art of Abysswalking.
Acquire the Lordvessel.
Arrive in Anor Londo.
Ring Bell of Awakening in Quelaag's domain.
Acquire the Rite of Kindling.
Ring Bell of Awakening at Undead Church.
Arrive in Lordran.
Acquire Estus Flask.
Light bonfire flame.