Mick Ronson's guitar heroics are gone.  Atmosphere triumphs over melody.  This is Bowie's first (although it would turn out not last) wholesale artistic makeover since he achieved stardom.  He defied expectation and challenged his listeners.  Not that there aren't melodies to be found, they are just obscurred by dense arrangements.  the clean bright sound of the ziggy period is gone and his sexually ambiguous personna is transforming into something more sinister and frightening.  this album is not an easy listen but it is most rewarding taken as a whole.