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