The "old" Woody was better than the "new" Woody MIP has some delightful moments but for the most part it's a disappointment in several ways. Woody Allen's earlier films, notably Love and Death (his best) were truly funny. He blended Marx Brothers slapstick with some genuine wit and gag humor and biting satire.
Now we have the "new" Woody, somewhat pretentious in his gray days, trying to mine old territory -- angst, neuroses, etc. -- but failing by not being very funny. Comedy is what reveals the human soul but here in MIP we merely get character sketches that may look good on paper but do not translate well to celluloid. Speaking of which, the camera Woody used to shoot this movie was terrible, producing artificial colors and failing to capture the charm of Paris, though he tried hard in the opening sequence. Soft pastel, less vivid imagery would have worked so much better.
Further, Woody badly misses the mark by pining for a "Golden Age" that was mediocre at best. Hemingway, Fitzgerald, et. al. were all second-raters (even Hemingway wrote bad Hemingway and is parodied to this day, which denotes his second-tier status). The 1920's may have been the gilded age in terms of wealth but when it comes to art, Woody was off by at least 30 years and might have found more inspiration from the Victorian Era and 19th Century when the true greats of literature and the other arts -- i.e., Dickens, Hardy, Eliot, Beethoven, Verdi, Goethe to name but a few -- stood well above anyone who lived and worked in the 20th Century.
As for the lead, Owen Wilson is all wrong for the part, but it's not his fault. Woody reworked the script to flesh out Wilson's character and therein lies in the problem. In his earlier films, Woody played the protagonist as financially struggling, angst- and guilt-ridden, a neurotic nebbish who knows that 2+2=4 but nonetheless worries about it constantly. Here, Wilson is rich, has rich would-be relatives and therefore has no money or status concerns. He's just a romantic, WASPish, hardly sympathetic or interesting, and he does not invite empathy. We don't really care about him like we did with Woody's earlier main characters who tried to come to grips with "the meaning of life." As for the other characters, they come off more like caricatures rather than real people. Hemingway is played strictly as parody (perhaps there is no other way to play him), and the Fitzgeralds were neither interesting nor likable. Gertrude Stein (Kathy Bates) is largely wasted.
Woody won an Oscar for a screenplay that was occasionally witty and clever but wit and cleverness are not enough. What was needed was more whimsy, drollery and belly laughs. MIP instead pokes you in the ribs now and then but not enough to elicit more than a smile now and then.