Entertaining Pulp Adventure by Veteran Author, John Shirley

A Sorcerer of Atlantis: with A Prince in the Kingdom of Ghosts has two key parts: (1) A three-chapter novel called "A Sorcerer in Atlantis" that has been released in doses over the years, and (b) the lost-world trip : "A Prince in the Kingdom of Ghosts", which despite its second billing, I enjoyed more.

First let's cover the author. To do that, I'll borrow from Douglas Draa who edited the 2020 release of Weirdbook #42: Special John Shirley Issue (~11 stories, including bits of those in this collection). Here's how Draa introduced John Shirley (who has written with several pen names):
“Seriously, Mr. Shirley is the recipient of multiple Bram Stoker and Locus Awards. He has won the International Horror Guild Award twice (along with 6 nominations). He has written two albums for Blue Oyster Cult, the original draft for The Crow, and been nominated for an Emmy for his work on the Teenage Mutant Ninja Turtles series. Oh! And he’s also scripted for Star Trek: Deep Space Nine!” – Douglass Draa Intro to WeirdBook #42

A Sorcerer of Atlantis - Publication History. This three-chapter novel has been published piecemeal. If you are looking for more Snoori and Brimm stories, they will probably be coming, but understand that the previous incarnations are essentially duplicated.

1) Jul 4, 2017, Swords Against Darkness, edited by Paula Guran
I. The Swords of Her Heart (by John Balestra)

1+2) Feb 26, 2020, Weirdbook #42: Special John Shirley Issue contains an entry called "Swords of Atlantis" which is really:
I. The Swords of Her Heart
II. Swords for the King

1+2+3) Jun 15, 2021, A Sorcerer of Atlantis: with A Prince in the Kingdom of Ghosts. With few changes, like the renaming of the Poseidon priest 'Mestor' to 'Nestor', we get a new chapter plus the previous two:
I. The Swords of Her Heart
II. Swords for the King
III. The Destiny of Atlantis

Without spoiling, the ending hints at another adventure set in Latina, Roma. That makes sense, since that would build on the strengths of this light-hearted read (focused on Atlantis to this point). The core milieu builds on tensions between Greek and Roman myths/history, namely between the sea-god Poseidon and the fire-appreciating Vulcanus. The call-outs to Roman and Greek gods are usually interesting (minotaurs, necropolises, volcano tubes under Atlantis) but are sometimes heavy-handed (Romulus and Remus make an unnecessary cameo).

The key strength is the fun environments, battle, and varied creatures. My favorites were the "Uncertain" demon trapped inside the Cold Heart of Jupiter and the demon "Zirrish." Expect lots of crypt walking and speaking with ghosts. That said, A Sorcerer of Atlantis is more comedic than immersive. The protagonist is Brimm the Savant, who is not only a suave barbarian but a competent magician. He’s both warrior (with his piercer sword) and mage so he can summon demons to do his bidding (like kill his enemies) if he can remember the spells. There is plenty of grand fights, but you’ll never feel like Brimm is actually in danger. Snoori is his foil, a compatriot who has a knack for escalating trouble. Romance is over-the-top melodromatic, with two royal women Selinn and Maitha fawning over Brimm. The first chapter reads like Fritz Leiber's Lankhmar series, with a fun duo fighting Lovecraftian horrors with swords & magic. The later chapters introduce a bunch of characters and enlarged the party such that it assumes more of an epic fantasy feel (classic S&S focuses on one hero).

Conflict? Brimm and Snoori are ostensibly after gold or honor (or something to pass the time). Thanks to Snoori's brilliant ideas, and Brimm going along with them, they are really causing troubles and then trying to fix them. Yep, most of their actions are damage control. Ultimately, Brimm's journey is really a coming-of-age story of a wanderlust dude who learns that he desires to protect others (Atlantis). It all starts with Cleito, and her presence and power extend through all three chapters.
And there, in an old palace [in Atlantis], awaits the beauteous Cleito, a princess who has offered ten bushels of gold to any ten men who will become the Swords of her Heart: the champions who will destroy a minor demon.” - Chapter 1

A Prince in the Kingdom of Ghosts: This entry is not Sword & Sorcery, but it is pulpy adventure that likely will satisfy the same readers. The light-hearted tone of Shirley pervades this story too. The protagonist Kerrin lives in contemporary times as a gem cutter, but is suddenly drug to a different world, one that promises to reveal the mystery of his father's sudden death (which happened when Kerrin was a teen). Kerrin's plight is more interesting than Brimm, and the weird descriptions a tad weirder (and more impactful) than the Atlantis adventure (which had decent settings actually). Anyway, here's two excerpts of the experience:

1) Kerrin looked over his shoulder at the palace... The gardens encircling the palace were varicolored, with enormous purple blossoms and vines with butter yellow blooms; then came a stand of trees with jade-like foliage. Along the edges of the avenue were nodding, diaphanous growths, some fifty feet high; translucent and drooping, their branches subtly moved of their own volition like the arms of sleepy Hawaiian dancers, slowly shifting gigantic translucent leaves. Light from the sparkling moon refracted by the broad lens-like leaves shattered into primary colors that fluxed with secretive dynamism. It made Kerrin think of an effect from light striking an inclusion deep within a polished diamond. As the phaeton trundled along, the light from the growths served as streetlamps, illuminating the road and an exquisitely serene pond of orange night-blooming waterlilies and golden lotuses, coming up on their left. The bordering lilies were artfully counterbalanced by swans, now easing toward their nests in the reeds. A small herd of deer cropped grass along the farther shore of the pond. Kerrin felt called, summoned by the light softly pulsing in the limpid water; by the living serenity of the place. He wanted to leave the phaeton and go to the pond, to sit in contemplation of it.

2) Illuminated by shafts of red light coming through the translucent stone at the peak of Bald Mountain was a squirming aggregation of ghosts. Specters in various stages of incarnation struggled like hundreds of white moths caught in transparent glue. They were fixed in a kind aspic of decaying caro spiritus—the source of the rancid odor underlying the smell of dead bats. Nearly three hundred spirits seemed entombed at Kerrin’s feet, in a putrefied melding of souls. Their faces were contorted with anguish, lined with misery, pinched by fear; their mouths were open in endless outcry. There were spirit countenances that had been Caucasian, African, Asian, Latino, Middle Eastern, all united by a cruel compression, a crushing constraint within their bonds. Kerrin could make out rag-ends of arms and legs, but not a complete body in the lot. Most of the fragmented ghosts were groaning, wailing, calling out in various languages for assistance. ( )