I got into Dan Greene through a used bookstore find years ago, and his genre blend was what hooked me. He doesn't really sit neatly in one category. I'd say he's known for speculative fiction with a heavy psychological thriller backbone. A lot of his work starts in a seemingly normal world—maybe a corporate office or a suburban neighborhood—and then he layers in these subtle, creeping elements of the paranormal or sci-fi. It's not full-blown fantasy with magic systems; it's more like the rules of reality just get a little... soft. The dread comes from characters realizing the world isn't what they thought.
His most famous book, 'The Quiet Echo,' is a perfect example. It's billed as a thriller about a man hearing voices, but the twist is deeply rooted in a kind of soft sci-fi concept about memory and time. That's his sweet spot: taking a very human, often psychological, conflict and viewing it through a slightly warped lens. You're never sure if the weirdness is supernatural or just a breakdown of the protagonist's mind, and he's brilliant at sustaining that ambiguity.
Some of his earlier stuff leaned harder into straight-up suspense, but even those had a speculative tinge. I wouldn't recommend him if you want pure, hard-boiled crime or epic fantasy. His genre is more of a mood—uneasy, thoughtful, and always questioning the nature of the reality his characters inhabit. It's a niche, but once it clicks for you, it's addicting.