I got into Koontz through my dad's old paperbacks, and the gateway drug for me was definitely 'Watchers'. It's got that classic Koontz formula—a brilliant dog, a genetically engineered super-being on the loose, and an ordinary guy caught in the middle. The pacing is relentless, and the bond between the man and the dog gives it a heart a lot of his other books lack. It's thrilling without being overly bleak.
From there, I'd jump to 'Lightning'. That one blends historical fiction with time-travel suspense in a way that feels unique for him. The central relationship drives the whole story, and it has a satisfying, almost hopeful arc that a lot of 80s horror-thrillers miss. 'Intensity' is another solid pick if you want pure, unadulterated adrenaline; it’s basically one long chase scene, but it’s executed so well you can't put it down. Avoid the doorstopper epics like 'The Face' or 'From the Corner of His Eye' for now—they can get a bit convoluted for a newcomer.
I have a soft spot for 'Winter Moon'. It's actually two novellas in one book, 'Strange Highways' and the title story. 'Winter Moon' is a creepy, isolated-farmhouse tale with an alien biological threat. It's claustrophobic and weird in the best way. Starting with a collection/novella combo like this gives you two distinct flavors of Koontz in one volume. You get the shorter, punchier 'Strange Highways' and the slower-building, atmospheric dread of 'Winter Moon'. It's a economical way to sample his range.
For a different angle, try 'The Husband'. It’s a contemporary thriller with no supernatural elements, just an ordinary man thrown into an impossible situation. The premise is simple and terrifying: a man is told his wife will be killed unless he pays an impossible ransom. It’s a masterclass in escalating tension and exploring what an average person is capable of under extreme duress. It’s lean, mean, and proves Koontz can write a gripping story without any speculative fiction hooks.