His novels have influenced modern horror in multiple ways. His concept of the 'Old Ones' and the idea that there are ancient, malevolent forces lurking beneath the surface of our world has inspired countless works. The way he made the familiar seem alien, like in 'The Shadow over Innsmouth' with the strange transformation of the townspeople, is now a staple in horror. His works have also led to a whole sub - genre of Lovecraftian horror that continues to thrive today.
They've had a huge impact. His use of cosmic horror, where the horror comes from vast, unknowable entities and the insignificance of humanity, has been widely copied. For example, many modern horror movies and books use the idea of a powerful, otherworldly force that humans can't really comprehend or fight against.