Where do you begin? You can pick up any Dean Koontz book you like and enjoy it as a standalone novel. However, he wrote two series that are enjoyed best when read in their correct order: The Odd Thomas books and the Frankenstein books. Odd Thomas is a gentle character with a quirky “super-power,” one he cannot control. If he gives himself over to it, it leads him where he needs to be to prevent a tragedy or solve a crime. If he attempts to force it, he may not only fail but also cause a tragedy for which he suffers greatly. The Frankenstein series is a sympathetic treatment of a man made monster (I could have written "man-made" - I didn't on purpose - think about it). Dean will make you think about Mary Shelley's monster in a whole new way.
Thank you, Mr. Koontz.