It did take me a while to get to like
Ubik. I was put off by the enigmatic ending, the first time I read it. Nowadays, I think the ending is what makes it all jell.
I second mike alexander's suggestion of checking out his short stories. Regarding his later work, much of it is semiautobiographical, and therefore more interesting when you've already got into the author, but
The Divine Invasion is an accessible exception.