WordNet sense 1 (completely lacking in playfulness):

unplayful

WordNet sense 2 (dignified and somber in manner or character and committed to keeping promises):

sedate, solemn, grave

WordNet sense 3 (concerned with work or important matters rather than play or trivialities):

serious

WordNet sense 4 (not inebriated):

unintoxicated

WordNet sense 5 (practicing complete abstinence from alcoholic beverages):

dry

WordNet sense 6 (lacking brightness or color; dull):

drab, somber, sombre

WordNet sense 7 (weak in color; not colorful):

colorless, colourless

WordNet sense 8 (become more realistic):

sober up