Subadi, I've never read Celestine Prophecy so I can't comment on that. But I can tell you that The Fifth Harmonic is one of FPW's best IMO... his other bests being Black Wind, An Enemy of the State, The Keep, and Deep as the Marrow. I don't really think T5H is classifiable genre-wise. It's sort of new-agey, but probably not in the sense you are thinking. I had no idea what to expect when I began reading (I had vague notions of something medical thriller/horror), and I was blown away by it.
In other words, do yourself a favor and read it!
Welcome to the board, BTW. My favorite FPW is his scifi.
Lisa