As you said, the book has many topics that it touches and it was interesting to see how what stood out for you the most is not what this book is about for me :) It might still be on the lines of partying, perhaps, but i couldnt stop thinking about the concept of 'lost generation' which Hemingway was part of and to me this book is about wasting time, not knowing what to do with their lives, and essentially it is a description of lost generation. People who lived after the WWI. (Ok, i just went to check the exact meaning of it, and in the wiki article it says that the term was coined by Hemingway as he used it in the epigraph to The sun also rises :))))))) Anyway, it only proves my point. I personally first learnt about it after reading The great Gatsby. And then in The sun also rises it was so evident - all these people are just lost in live.