This movie causes the audience to consider many topics on morality, particularly the poor choices made by the Joker. The Joker is more relatable in this movie than antagonists usually are. I think this gives a more realistic view of "bad" people, who are not usually 100% bad in all ways as society often judges. It is important to know when to sympathize with the Joker (towards the beginning of the movie), and when he needs to be identified as a threat (when he begins making certain bad choices). This movie is only suitable for adults who are willing to pick it apart and think critically about it. It isn't for light amusement. That substance is what makes it so good.
If you aren't able to ponder underlying themes on your own, and you have to be handed all your thoughts to you, then this isn't the best movie for you.
If you aren't able to ponder underlying themes on your own, and you have to be handed all your thoughts to you, then this isn't the best movie for you.