I don't reccomend Valis for anyone but the most diehard Dick fans. Its an attempt to fictionalize an experience Dick had and spent the rest of his life trying to understand. It has some great moments, but it doesn't hold together terribly well as a story. I much prefer more focused stories like Scanner Darkly, Flow My Tears, or even Divine Invasion.

Supposedly Dick's experience conceived three published novels--Valis, The Transmigration of Timothy Archer, and Divine invasion. There is a fourth, unpublished novel--Radio Free Albemuth that came from it as well. Valis seem to be the most personal since it someone named Philip Dick (or Horselover Fat) having the exact same experience then trying to make sense of it. Divine Invasion has more of the feel of a traditional Dick novel with someone forced to live in a hovel on an alien planet. Timothy Archer is borderline non-SciFi, with only a tiny influence of SciFi, IIRC. And Radio Free Albemuth felt a bit like a cross between Scanner Darkly and Valis--i.e. the Valis story in a dystopian future surveilance state.