This is a fantasy romantic comedy. It's fantasy because there is time travel that is never explained; but it doesn't need to be explained as the movie is not really about that. It's about Gil & his love life, his life in general, actually. It's a very light movie with nothing terribly obvious or forced.
Having read a number of books by Fitzgerald & Hemingway, I always forget that they actually knew each other & so did the other artists in the movie. It's a fun movie where you get to watch what those artists may have been like with each other as a modern day writer, Gil, befriends them. Of course it's a movie, not a documentary so they obviously may not have behaved that way but it still made me want to read more of their books & watch "The Exterminating Angel." I was never in love with Paris & even after watching the movie it's still just another city to me. But this movie I liked a lot. It isn't clear why Owen Wilson is engaged to Rachel McAdams, I'm guessing because he is successful enough as a screenwriter to get an attractive blonde who only cares about money. I never noticed how perfect Owen Wilson is for playing the Woody Allen role.
You will enjoy it a lot more if you've read their books & are familiar with their art.