It is just that he seems to like a particular character type. It isn't that his characters are shallow are underdeveloped it is just that his lead male and his lead females characters are a little to similar. His lead character is always this sort smooth dude who listens to cool non mainstream music and has the easy laid back relationship the lead female character who also has a love for the same type of music. They are not bad characters I just think he relies on the type to often and it makes his books seem to similar.