Answer:
From my point of view, justice has not been served, specially if we understand that revenge is not a synonym of justice. Moreover, the ending has a bittersweet sensation because one would have expected someone to survive and find a way of restoring the order; with the death of King Claudius and Prince Hamlet, Denmark is left in a fragile situation, and we wonder: Was this Hamlet's plan? How could this be justice when there is not a complete positive outcome for Hamlet and the society?
We should consider the different events of the play, because there are several characters that are seeking revenge/justice. In the final scene, we can see that:
From this point of view, it could be said that revenge is the only protagonist of this play. If any of the characters would have been able to leave their personal affairs aside, they could have thought of the consequences that could be left for the people around them. Their thirst for revenge only left them satisfied, and the rest suffered the consequences. If they would have sought justice, the outcome would have been different: order would have been re-established and Denmark wouldn't have been left on such fragile situation.
