What the overall theme of the great gatsby?

The main plot is about a man and woman falling in love. However, if you go deeper in the story it's basically showing how the "American dream" or any dream is unattainable. During this time, the 1920's, people went against their morals such as Jay Gatsby and did what they could to become successful. But as much as they tried they still were unhappy. Like how Jay was wealthy and successful but just wanted to be with his love Daisy. He ended up unhappy because his true dream was short-lived. Hope that wasn't too confusing.