The Great Gatsby is a beautifully written short book; a tale about the entanglement of the worthy with the worthless and how you can never turn back the clock. The title character appears superficial but there is a deeper reason for his extravagant parties. Gatsby, despite his underworld business interests, is quite sympathetic even if the narrator doesn't think so.
There's no happy ending but it's all highly believable and the characters act just as you might expect them to in real life. I don't think it should be taken as social commentary; it's a simple story of quixotic love and how, in the end, women usually prefer the devil they know.