Prince of the Undying by Karen Kincy is a thrilling entry into the realms of fantasy and supernatural dynamics entwined with the nuances of power, ambition, and human frailty. This novel, folding in elements of romance alongside a dark and enthralling plot, forges a path into a world where the familiar tussles with the mystical, captivating readers who thirst for narratives steeped in magical realism and visceral undertakings.

The story revolves around Elaria, a young necromancer who discovers her blood holds the key to eternal life. She lives in a world where her kind is hunted and despised, feared for the powers they wield over death itself. But more than fear, there’s envy in the eyes that follow her, for controlling death is akin to controlling the cornerstone of power in Kincy's elaborately crafted universe. Elaria's journey is exacerbated when she encounters the enigmatic and dangerously alluring Prince Nocturne, an immortal with a thirst for a freedom that only she can unlock.

Karen Kincy’s structured world-building deserves high praise—it’s meticulous, vividly painted, and serves as a lush backdrop for the character-driven drama that unfolds. The stark delineation between the regions of the Undying Lands and the mortal realms offers not just geographic diversity but also sociopolitical conflict, a fertile ground for the narrative seeds that Kincy sows with adept hands. It serves to provide a thorough exploration into the ways in which power can corrupt absolutely and the lengths to which individuals will go to seize it or, conversely, to thwart its accumulation.

The character of Elaria is well-fleshed out, embodying both the tenacity and vulnerability inherent in being perceived as a pariah within her own world. Her growth, from a skittish necromancer to a formidable force reckoning with the expansive and often ruthless powers at play, is rendered with both compassion and rigor. Her relationship with Prince Nocturne evolves beautifully—from cautious allies to passionate, albeit conflicted, lovers. Their dynamics are tinged with an intensity that both draws and repels them, serving as a vibrant core to the swirling drama around them.

Moreover, Prince Nocturne is not merely a titular character but a pivotal axis around which the story spins. His portrayal is multifaceted—he is, by turns, charismatic and menacing, a creature of darkness that yearns for light. The author masterfully plays with the dichotomy of life and death, embedding it into the characters' identities and thereby elevating the novel from a simple supernatural tale to a profound exploration of existential motifs.

The secondary characters are not to be overshadowed, either. Each supports the overarching themes of loyalty, betrayal, and the quest for power. From wise, old mentors to gleefully malicious villains, the cast is diverse and effective in their roles, enhancing the main narrative and providing depth and additional layers of intrigue to the storyline.

Kincy’s prose is another element that deserves recognition. It is both lyrical and sharp, weaving descriptions that are as striking as they are sublime. The dialogue, while sometimes veering towards the archaic, fits well within the constructed world and adds to its authenticity and charm. There are moments where the pacing might feel uneven—particularly as Kincy sets up her world’s intricate politics and lore—but the climax is both rewarding and thought-provoking, making any prior sluggishness worth the wait.

Critically, while Prince of the Undying delivers on many fronts, it might not escape censure for certain tropes that veer dangerously close to cliché. The love story, central as it is, occasionally treads familiar ground and might benefit from a fresher take. Nevertheless, it is the novel’s dark undertones and the moral ambiguities it presents that keep the narrative engaging and provocative.

In essence, Karen Kincy’s Prince of the Undying is a commendable fantasy that tantalizes and terrifies in equal measure. It plunges the reader into an abyss of moral quandaries and out through the crescendo of an operatic power struggle. Definitely a recommended read for those who find solace and thrill in the nocturne of undying realms and unyielding desires.