Watchers is good. If you can get a copy of Twilight Eyes, pick that one up. It's the best of Koontz. The Moonlight Cove twosome is pretty good for recent books, From the Corner of His Eye is pretty decent, I think.
I wasn't really hooked on False Memory, though.
Tick Tock, the first time I read it, I hated. The second time I read it, I loved it. It's a "genre" book, written in a whole different style than Koontz's other works.
Strange Highways was really good.