I really enjoyed the book. I've always thought of it as being about the pearls of obsession and becoming what you pursue.
Daisy represents everything Gatsby wants to become, rich, attractive, popular. In his idealised obsession with her he creates a world in which he can become her equal.
As the story unfolds it become more apparent that Daisy is without substance, she is shallow, flakey, easily led and so on. Gatsby by the end is revealed as a deceitful construct; a mirror that reflects the wealth and charm of others. When all is said and done he has become Daisy's equal.
Just my 2p.