He Sees You When You're Sleeping by Haley Tyler navigates through the crevices of the thriller genre, twisting a typical narrative into a haunting ballet of suspense and surprise. Tyler, an adept storyteller, leverages her unique voice to ensnare readers into a tale that is as much about psychological torment as it is about unbridled terror.

At its core, the novel introduces us to Carol Simmons, a young woman who has recently moved into her new apartment in a seemingly benign urban sprawl. The book's title is a creepy precursor to the unraveling events centered on the theme of being watched—the quintessential nightmare in an era where privacy is often digitally disrupted. However, Tyler's approach is far from cliché. Instead, through Carol’s interactions and the mysterious elements of her apartment, readers are pulled into a visceral experience of paranoia and isolation.

The narrative is smart and edgy, balancing on the thin line between reality and Carol's possibly fractured perception of it. Tyler excels in building a scenario where every creak and whisper in Carol's apartment pulsates with menace, effectively blurring the line between paranoia and genuine threat. It is the ambiguity of this threat that strengthens the tale, compelling the reader to sway between sympathy and suspicion towards Carol. Her internal monologue, expertly laid out by Tyler, adds layers to this dilemma, enhancing the psychological depth of the narrative.

Aside from Carol’s intensely portrayed psyche, the supporting characters are equally intriguing. The enigmatic neighbor, Mr. Dobbs, who oscillates between avuncular and creepy, adds a deliciously unsettling contrast to the story. His interactions with Carol are fraught with an uncomfortable tension that Tyler exploits to full effect, driving the plot forward with a series of chilling encounters. Meanwhile, Detective Hanover offers a semblance of sanity and safety though his own complexities ensure that the reader’s feet never quite touch solid ground.

Tyler's prose is meticulous and evocative. She possesses a keen eye for detail—be it in the vivid descriptions of the setting, which almost becomes a character on its own, or the nuanced observations of human behaviors under duress. Dialogue is another of Tyler's strengths, realistic and sharp, often piercing the mood with its truth.

The plot twists in He Sees You When You're Sleeping are clever and unpredictable, propelling the story with enough force to keep the pages turning fast. As the suspense builds, Tyler masterfully drops breadcrumbs, keeping the readers guessing the identity and intention of the watcher. When the climax arrives, it is both satisfying and startling—no small feat in a genre often burdened with predictable outcomes.

However, the novel does leave some desires in its wake. While the conclusion is explosive and generally fulfilling, certain revelations might feel slightly rushed, leaving a rare few questions insufficiently answered. This might be the byproduct of the novel's otherwise relentless pacing, and hardly detracts from the overall enjoyment, but those who like every loose end tied might find themselves going back a few pages to track the hints dropped earlier.

Thematically, Tyler doesn’t shy away from deeper existential ruminations. Through Carol’s ordeal, He Sees You When You're Sleeping explores the broader societal and personal implications of surveillance. The psychological intrusion of being watched, or even the fear thereof, is paralleled with the erosion of identity and autonomy—a poignant reflection in our times of digital oversharing and privacy erosions.

In conclusion, He Sees You When You're Sleeping by Haley Tyler is a compelling read that skillfully interweaves elements of psychological thriller and horror to explore deeper themes of privacy, identity, and madness. Haley Tyler proves herself a deft crafter of narratives that chill and thrill, leaving her readers eagerly waiting for what she will write next. This book, with its rich characterization, sharp plot twists, and palpable suspense, is surely destined to be a favorite on the shelves of those who cherish a good thrill.