Having read Order 66, I feel that I must strongly recommend against it. I can't speak for the others [in the series], but I've heard quite a bit of criticism for True Colors, as well.
"Grant Allen [...] had written a book about the Evolution of the Idea of God. [...] it would be much more interesting if God wrote a book about the evolution of the idea of Grant Allen." ~ G. K. Chesterton, The Everlasting Man