I have read nearly all what the former reviewers said. I agree with much of it. What can I add?
First, I'd like to say that there is a lot of symbolism in this movie. The producer meant every thing he did in it. Nothing is done randomly. For example the choice of black and white (no colours) states clearly that our lives can shift within these two colours Black (sadness) and white (smile-happiness). They have to exist together. they fight each other. We are the ones to choose which side to take. This is the old philosophical debate of good and evil.
Second, I think that the movie tells us that what ever our social class, our financial situation or where ever we are we can either influence others positively or negatively. We have seen the cheerful park attendant turn many sad people into happy one, from simple citizens to countries'presidents and also the opposite: we have seen the same person turn the same people from happiness to sadness because that is what he was living at that moment.H just communicated it. So Every one counts in this world.
Thirdly, He made happy many people but he didn't succeed to make the photographer smile. What ever he did. However, she smiled at him at the end and he didn't even know how she did it. This episode teaches us no to give up but continue our fight because thing change in a way or in an other.
To conclude, as I am a teacher of English language, I will try to use this video in classroom, and I hope it will bring a lot of my student to this web site and post their reviews.