WordNet sense 1 (earnest):

dear, devout, heartfelt

WordNet sense 2 (open and genuine; not deceitful):

sincere

WordNet sense 3 (characterized by a firm and humorless belief in the validity of your opinions):

solemn

WordNet sense 4 (concerned with work or important matters rather than play or trivialities):

serious

WordNet sense 5 (not distracted by anything unrelated to the goal):

businesslike

WordNet sense 6 (serving as or indicating the existence of a purpose or goal):

purposeful