So Midnight In Paris is about a couple, Gil and Inez, who are just kind of traipsing around Paris on the heels of Inez's father. The couple is engaged to be married and clearly don't belong together from the start - except that they are both absolutely beautiful. This is sort of why you forgive Rachel McAdams for being such a bitch - because she is over the top hot.
Anyway, Gil is of course a lost and philandering writer who wants to make a piece that is meaningful. He is very much so focused on the past and what he believes were "The Golden Years" or the roaring 20's if you prefer. While hitting tourist hot-spots around the city, they run into Inez's old flame, Paul.
Paul is a genius as luck would have it, he knows everything about everything. His wife follows him around like a puppy dog drooling over every word, and Inez does her one better by telling Gil to shut up so she can better listen to Paul at every turn.
Of course, Gil, makes a run for it when invited out dancing with Paul and his wife. As he gets himself lost in the city, wandering alone at midnight - magical things begin to happen...
Gil is transported to the 20s where he meets the Fitzgerald's, Hemingway, Gertrude Stein, Picasso, and his lover Adriana. He has the time of his life, he puts his own writing in perspective, he suggests ideas to the great thinkers, and he falls in love.
Of course, the point is that we all have a golden era we wish to bask in, to help us forget our economy, our politics, etc. So nothing is ever eternally blissful enough. However, this movie is just great enough for a literary nerd to forget all that crap for a minute or two anyway.