More than a game, "To The Moon" is a vessel that will take you somewhere you forgot about.
You do not play "To The Moon" as a game, or at least you should not try. It even makes a very successful joke about this early in the story.
The expression "interactive story" is much better suited here. And the beauty of it is the way it moves you along during its course. It will take you some places you have not visited in a while, it will make you realize the impact of past events and will give you this gentle push you might need to create a better future.
All in all, this experience is extremely personal, more than any story I have read or seen in a game before. Only once the credits have faded will you realize Johnny and his memories have everything to do with your own life.
Let yourself be moved by this masterpiece and ... enjoy your life!