The Wall Street Journal's Joe Morgenstern liked it, John Podhoretz at The Weekly Standard didn't (no link available). Me? I seldom go to movies. But when I do, it's usually because of the concept or subject. The last Woody Allen movie I remember seeing was his 1975 "Love and Death," demonstrating that I'm not a big fan. But his latest flick, "Midnight in Paris" (IMDb link here) intrigued me due partly to its time-travel gimmick and mostly because it includes writers and artists of Paris in the 1920s, a period I've read a fair amount about (that's the movie's Zelda Fitzgerald at the left in the photo above). So I went.
Read Morgenstern's review for details about the movie. I'll just name-drop. There are major speaking parts for Ernest Hemingway and Gertrude Stein, lesser ones for Pablo Picasso, Salvador Dalí (who is obessing on the concept of "rhinoceros"), Luis Buñuel (in need of movie ideas), Man Ray, Scott and Zelda Fitzgerald (she attempts suicide at one point), T.S. Eliot, Henri Matisse, Henri de Toulouse-Lautrec, Paul Gauguin, Edgar Degas (the last three in a secondary time-warp), and a singing part for Cole Porter.
The casting director did a good job finding actors who could be made up to look a lot like the originals. Since you can't win 'em all, there were some compromises. For example, Picasso might have been a bit too tall and slender, and Man Ray definitely was too tall. But you watch it and find more near-misses, though that probably won't interfere with your experience.
A character in the 2010 part of the movie is a know-it-all who disputes facts with the guide at the Rodin museum; that one hit pretty close to home. The guide, by the way, was played by France's femme No. 1, Carla Bruni.
There also were some temporal ambiguities. Hemingway was encountered after his first novel (1926) but before he wrote much more. Dalí was in Paris in 1926, but Surrealism was largely a literary movement at that time, its better-known painting/visual aspect was only starting to emerge even though much is made of it in the movie. Those points and others make it difficult to pin down just when in the 20s the action takes place. But again, that's minor because Allen is trying to evoke a short, rich era rather than any particular time within it.
So if you like arts and letters and have more than passing knowledge of Paris and the 1920s, you'll likely find much in this movie to enjoy.