The above linked article talks about fantasy series that are worth starting. I have several of the books in many of these series. Some are on my TBR list, some have been started. One of these days I’ll get to them.
ACACIA BY DAVID ANTHONY DURHAM
Where to Start? Acacia: The War with the Mein
AEGIS OF THE GODS BY TERRY C. SIMPSON
Where to Start? Etchings of Power
ARTHURIAN SAGA BY MARY STEWART
Where to Start? The Crystal Cave
AVALON BY MARION ZIMMER BRADLEY
Where to Start? Mists of Avalon
THE BOOK OF THE NEW SUN BY GENE WOLFE
Where to Start? The Shadow of the Torturer
THE BROKEN EARTH TRILOGY BY N.K. JEMISIN
Where to Start? The Fifth Season
THE BROKEN EMPIRE BY MARK LAWRENCE
Where to Start? Prince of Thorns
THE CASTES AND THE OUTCASTES BY DAVIS ASHURA
Where to Start? A Warrior’s Path
CHRONICLES OF ELANTRA BY MICHELLE SAGARA
Where to Start? Cast in Shadow (there are several prequels, but this is book 1)
Finished? No, but 12 are published, so plenty to read!
CROWN OF STARS BY KATE ELLIOTT
Where to Start? King’s Dragon
THE DANDELION DYNASTY BY KEN LIU
Where to Start? The Grace of Kings
Finished? No. First 2 published.
THE DARK TOWER BY STEPHEN KING
Where to Start? The Gunslinger
DEVERRY BY KATHARINE KERR
Where to Start? Daggerspell
DISCWORLD BY TERRY PRATCHETT
DRAGONLANCE BY MARGARET WEIS AND TRACY HICKMAN
Where to Start? Lots of places to begin. I started with Dragons of Autumn Twilight, which is also the first the pair wrote.
Finished? Yes and no. Weis and Hickman still publish books in this universe, but there are PLENTY of completed trilogies within the universe.
EARTHSEA CYCLE BY URSULA K. LE GUIN
Where to Start? A Wizard of Earthsea
EARTHSINGER CHRONICLES BY L. PENELOPE
Where to start? Song of Blood & Stone
Finished? No. First 2 complete.
ELRIC BY MICHAEL MOORCOCK
Where to Start? Elric of Melnibone
ETERNAL SKY BY ELIZABETH BEAR
Where to Start? Range of Ghosts
FARSEER TRILOGY BY ROBIN HOBB
Where to Start? Assassin’s Apprentice
THE FIRST LAW BY JOE ABERCROMBIE
Where to Start? The Blade Itself
GENTLEMAN BASTARDS BY SCOTT LYNCH
Where to Start? The Lies of Locke Lamora
Finished? No. First 3 published.
GORMENGHAST BY MERVYN PEAKE
HERALDS OF VALDEMAR BY MERCEDES LACKEY
Where to Start? Lots of entry points. Chronological: Arrows of the Queen. My favorite trilogy in this universe begins with Magic’s Pawn. If you want a stand-alone in this series to see if you want to continue, read By the Sword.
KINGDOMS OF THORN AND BONE BY GREG KEYES
Where to Start? The Briar King
THE KINGKILLER CHRONICLE BY PATRICK ROTHFUSS
Where to Start? The Name of the Wind
Finished? No. First 2 published.
KUSHIEL’S LEGACY BY JACQUELINE CAREY
Where to Start? Kushiel’s Dart
LONG PRICE QUARTET BY DANIEL ABRAHAM
Where to Start? A Shadow in Summer
THE LORD OF THE RINGS BY J.R.R. TOLKIEN
LYONESSE BY JACK VANCE
Where to Start? Suldrun’s Garden
MILLENNIUM’S RULE BY TRUDI CANAVAN
Where to Start? Thief’s Magic
Finished? No. First 3 complete.
NEW CROBUZON BY CHINA MIÉVILLE
Where to Start? Perdido Street Station (though I actually read these completely out of order the first time and had no problem).
OBSIDIAN AND BLOOD BY ALIETTE DE BODARD
Where to start? Servant of the Underworld (there are several prequels, but this is book 1)
OLONDRIA BY SOFIA SAMATAR
Where to Start? A Stranger in Olondria
Finished? Probably (only 2 books in the series, and both are stand-alone)
PAKSENARRION BY ELIZABETH MOON
Where to Start? Sheepfarmer’s Daughter
Finished? Yes, though she continues to write in this world on a regular basis.
RETURN TO NEVÈRŸON BY SAMUEL R. DELANY
Where to Start? Tales of Nevèrÿon
RIDDLE-MASTER BY PATRICIA MCKILLIP
Where to Start? The Riddle-Master of Hed
SEVENWATERS BY JULIET MARILLIER
Where to Start? Daughter of the Forest
A SONG OF ICE AND FIRE BY GEORGE R.R. MARTIN
Where to Start? A Game of Thrones
Finished? Notoriously no, but the first 5 are completed.
THE SORCERER OF WILDEEPS BY KAI ASHANTE WILSON
Where to Start? The Sorcerer of Wildeeps
Finished? Maybe. Two so far, both stand-alone novellas in the same universe. Will there be more? We can only hope.
THE STORMLIGHT ARCHIVE BY BRANDON SANDERSON
Where to Start? The Way of Kings
Finished? No. First 2 published, 3rd coming in November (it’s currently listed as a 10 book series on Goodreads).
THE SUNBOLT CHRONICLES BY INTISAR KHANANI
Where to Start? Sunbolt
Finished? No. 2 published so far.
SWORD OF TRUTH BY TERRY GOODKIND
Where to Start? Wizard’s First Rule
Finished? I think he plans to continuously add books to this series forever. For. Ever.
TAMÍR TRIAD BY LYNN FLEWELLING
Where to Start? The Bone Doll’s Twin
TENSORATE BY J.Y. YANG
Finished? No. First 2 novellas published.
TEMERAIRE BY NAOMI NOVIK
Where to Start? His Majesty’s Dragon
THE WHEEL OF TIME BY ROBERT JORDAN AND BRANDON SANDERSON
Where to Start? The Eye of the World
Finished? Yes. Finished posthumously by Brandon Sanderson
WORLDBREAKER SAGA BY KAMERON HURLEY
Where to Start? The Mirror Empire
Finished? No. Final book in the trilogy comes out next year.
THE WORLD OF RIVERSIDE/TREMONTAINE BY ELLEN KUSHNER AND MANY OTHER AUTHORS
Finished? Kind of. The original The World of Riverside series is complete, but Tremontaine is still going!
WORLD OF THE FIVE GODS BY LOIS MCMASTER BUJOLD
Where to Start? The Curse of Chalion
Finished? Kind of. The first 3 can work together as a trilogy, and are completed. She’s been adding novellas to the series with Penric’s story.