What is the author's tone in Mystery Train: Images of America in Rock 'n' Roll Music by Greil Marcus?

Marcus' tone is very subjective. Although he often uses information he has gotten personally from the artists themselves about their reasons for writing their music, Marcus injects his own opinions about the music and the political atmosphere of the time period in order to draw his own conclusions about the impact each artist made with his music. Since Marcus lived during the time period when the music was being created, he is also able to use his store of personal information about the time period in order to create his own opinions.