Being a huge Xavier fan from the first time I heard him, I have to admit that Dark Shades of Blue is a definite departure from his previous work (and after a number of listens is finally growing on me).
For first time listeners I'd recommend you start the way that I did, with his first album 'To Let' and work through his other albums before landing on DSOB, that may give you a much greater appreciation for what an amazing talent this man is.
Plus, if you ever have a chance, take in a live show and you will become an instant fan.