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.
Acquire all rare weapons.
Discover Princess's Guard covenant.
Discover Blade of the Darkmoon covenant.
Reach "The Dark Lord" ending.
Acquire best weapon through magic reinforcement.
Acquire best weapon through enchanted reinforcement.
Acquire best weapon through crystal reinforcement.
Acquire best weapon through divine reinforcement.
Defeat Dark Sun Gwyndolin, the Darkmoon God.
Acquire best weapon through fire reinforcement.
Acquire best weapon through chaos reinforcement.
Acquire best weapon through occult reinforcement.
Acquire best weapon through raw reinforcement.
Acquire best weapon through standard reinforcement.
Acquire the Rite of Kindling.
Discover Gravelord Servant covenant.
Discover Darkwraith covenant.
Defeat Crossbreed Priscilla, the Lifehunter.
Reach "To Link the Fire" ending.
Defeat the Soul Lord Gravelord Nito.
Defeat the Soul Lord Bed of Chaos.
Acquire best weapon through lightning reinforcement.
Discover Path of the Dragon covenant.
Defeat Seath the Scaleless, inheritors of souls.
Discover Warrior of Sunlight covenant.
Defeat the Four Kings, inheritors of souls.
Acquire the Art of Abysswalking.
Discover Forest Hunter covenant.
Acquire the Lordvessel.
Arrive in Anor Londo.
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.
All achievements completed. Congratulations!
Acquire all sorceries.
Acquire all pyromancies.
Acquire all miracles.