Disgruntled usually describes negative feelings; it's rarely used in a positive or neutral context. The disgruntled audience booed after the show was abruptly cancelled.
Pro Tip 2/3
Subtle Intensity
While 'disgruntled' indicates dissatisfaction, it's less intense than being furious or enraged. After waiting an hour, the disgruntled customer calmly asked for a refund.
Pro Tip 3/3
Personal Discontent
'Disgruntled' often relates to personal grievances rather than large, public issues. He became disgruntled after being passed over for a promotion yet again.