Diablo II: Resurrected

There are 27 Act Quests in all. They are easy to find in the in-game menu and (mostly) simple to complete by following the given instructions, but it's possible to finish the game with a few left uncompleted. Note that you need to play in Expansion Mode to get them all. For this achievement, all quest icons need to go from blacked out (undiscovered) to colored (active) to grayed out (complete).

Following is a brief description of all Act Quests. I'll leave out obvious details like who gives the quest and who to speak to at the end unless it isn't obvious (look for "!" above npcs in camp to get quests and follow instructions in the quest menu to complete). Those that are possible to pass by are in bold and those that are most commonly missed are also underlined:

Act I
1 - The Den of Evil: Kill every enemy in the Den of Evil (in Blood Moor).
2 - Sisters' Burial Grounds: Kill Blood Raven, found in Burial Grounds (area connected to Cold Plains).
3 - Search for Cain: Find Tree of Inifuss (in Dark Wood) and grab the Bark Scroll. Find the five Cairn Stones (in Stony Field) and use the scroll to activate the stones in the correct order to create a portal to Tristam. Find and free Deckard Cain in Tristram.
4 - The Forgotten Tower: Find and read the Moldy Tome (in Stony Field). Enter The Forgotten Tower (in Black Marsh) and descend to level 5 to kill the Countess.
5 - Tools of the Trade: This is given by Charsi after saving Deckard Cain. Find and kill The Smith in the Barracks (connected to Outer Cloister) to retrieve The Malus. Have Charsi imbue an item to complete.
6 - Sisters to the Slaughter: Kill Andariel in the fourth level of the Catacombs.

Act II
1 - Radament's Lair: Enter the Sewers under Lut Gholein and kill Radament on level 3. Make sure you pick up the Horadric Scroll.
2 - The Horadric Staff: Take the Horadric Scroll to Deckard Cain. Find the Horadric Cube on level 3 of the Halls of the Dead (in Dry Hills). Find the Horadric Shaft in the Maggot Lair (in Far Oasis). Find the Horadric Amulet on level 2 of the Claw Viper Temple (in Valley of the Snakes). Use the Horadric Cube to combine the Shaft and the Amulet.
3 - The Tainted Sun: After entering the Lost City, where everything goes dark, talk to Drognan in town. Destroy the altar on level 2 of the Claw Viper Temple (same room as Horadric Amulet)
4 - The Arcane Sanctuary: Descend to the Palace Cellar to find the portal to the Arcane Sanctuary. Find Horazon's Journal there.
5 - The Summoner: Kill the summoner in the Arcane Sanctuary (he guards Horazon's Journal).
6 - The Seven Tombs: Pay attention to the symbols that light up near Horazon's Journal in the Arcane Sanctuary. Whichever one is missing will be at the entrance of the correct tomb (compare the group to the full set of seven symbols found on the ground nearby to figure it out). Go through the portal and find that tomb somewhere on the edge of the canyon. Enter the tomb, find the Orifice, and insert the Horadric Staff. Enter the passage that opens and kill Duriel.

Act III
1 - The Golden Bird: Continue killing enemies in the Spider Forest until a Jade Figurine drops. Take it back to Deckard Cain, then to Meshif, who will give you a golden bird to take to Alkor. Return to him after several seconds.
2 - Blade of the Old Religion: Speak to Hratli. Find the Gidbin Blade in the Flayer Jungle.
3 - Khalim's Will: Find Khalim's Eye in the Spider Cavern (in Spider Forest). Find Khalim's Brain on level 3 of the Flayer Dungeon (in Flayer Jungle). Find Khalim's Heart in the Sewers (in Kurast Bazaar). Find Khalim's Flail in Travincal. Combine all four in the Horadric Cube to create Khalim's Will, which you will use to destroy the Compelling Orb in Travincal.
4 - Lam Esen's Tome: Find Lam Esen's Tome, which is somewhere in one of Kurast's six temples (two in Lower Kurast, two in Kurast Bazaar, two in Upper Kurast).
5 - The Blackened Temple: After entering Travincal, speak to Alkor. Kill all members of the High Council in Travincal.
6 - The Guardian: Kill Mephisto on level 3 of the Durance of Hate.

Act IV
1 - The Fallen Angel: Kill Izual (in Plains of Despair).
2 - The Hellforge: Destroy Mephisto's Soulstone on the Hellforge (in River of Flames).
3 - Terror's End: Kill Diablo in the Chaos Sanctuary.

Act V
1 - Siege on Harrogath: Kill Shank in the Bloody Foothills. Have Larzuk socket an item to complete.
2 - Rescue on Mount Arreat: Rescue Qual-Kehk's men, which are in three groups in the Frigid Highlands.
3 - Prison of Ice: Find Anya (in Frozen River). Return to town to speak with Malah, who gives a special thawing potion you can use to free Anya.
4 - Betrayal of Harrogath: Use Anya's portal and kill Nihlathak on level 3 of his temple. Have Anya personalize an item to complete.
5 - Rite of Passage: Activate the altar in Arreat Summit and kill the 3 Ancients.
6 - Eve of Destruction: Kill Baal's Guardians in the Throne of Destruction (from level 2 of Wolrdstone Keep), then kill Baal in the Worldstone Chamber.