The Great Gatsby
I think the biggest surprise about The Great Gatsby was what a pleasure it was to read; not what you expect of the "great" classics you are happy to not be required to read with your school days finished. It's fast paced, not long for a novel, with completely natural dialogue. The prose is gorgeous and memorable and leaves you with an indelible impression of the Jazz Age.
It has a reputation as a romantic book, or as a romance I don't think is justified. Daisy Buchanan and Jay Gatsby come across to me as too shallow for me to believe in the sincerity or deepness of their affections. But then I think that's part of what the book is about: surface versus reality and flash versus substance. Daisy is more an ideal of romance Gatsby flirts with and Gatsby himself all shining facade.
Americans like to think of themselves as "self-made" and if The Great Gatsby is thought of as a great American novel I think it's partly because in the figure of Gatsby you get the fake side of that--not someone who sheds past or tradition to become a truer self but to hide their real self--and because he can't it comes crashing down.
But the book itself isn't shallow or just surface shine but the kind you find more that strikes you on rereads. I think that might be part of why it's Nick Carraway that carries the narrative, not Gatsby. You need an observer deeper and sharper than Gatsby and the observer perspective allows Gatsby to be introduced (a good 54 pages into the book in my edition) as a mysterious figure you get to know from the outside surface in.