I thoroughly enjoyed this movie, but it is nothing new.
Everyone here is grouping it with other war movies, this movie has been miscategorized! Its not a war movie any more than "One flew over the cuckoos nest" is a asylum movie or "Cool Hand Luke" is a prison movie. This is a movie about individuality, nonconformity, self-confidence and the costs of that personality type.
The plot is the same as "One flew over the Cuckoos nest" and "Cool Hand Luke", its in GOOD company, and it holds its own. Its these movies it should be held up against and compared, not "Apocalypse Now" or "Platoon".
Eric

(various spoilers follow)
Gene Kelly. Not Georges Guetary, who is sometimes criticized for being too young and un-French. Not Leslie Caron, who is sometimes criticized for her very green performance. Not even Oscar Levant, who more often than not annoys the dickens out of me.
No, it would definitely be Gene Kelly. There's something about his screen persona that's too ambitious and focused for him to be convincing as a penniless artist in Paris, content to put off facing the critics indefinitely, frolicking with little kids and old ladies and painting in the streets. That's what made him so effective in SINGIN' IN THE RAIN and other movies where he played ambitious, focused characters. Jerry Mulligan is in some ways a cousin to Tommy Albright in BRIGADOON, another Lerner story with Kelly miscast as an American at loose ends who falls in love with a picturesque European place and an innocent female who embodies its virtues.
Except that Jerry isn't as likeable as even poor dazed Tommy. That's another galling thing about this film. Jerry is sometimes a cad to Milo, and even worse to Lise. When he first sees the latter at a club, he pulls a dirty trick to get her to dance with him. When she sits down again he pulls an even dirtier trick to get her phone number. When he calls her the next day she hangs up on him, which he takes as a cue to drop in at her workplace. And throughout all this it's obvious she wants NOTHING to do with him. When she starts laughing at his jokes in the perfume shop, it's about as believable as Milo's interest in his paintings. Sure he's good-looking and playful, but why should that sway her when she's got Henri, who seems like a gentleman to boot?
Admittedly it comes off so distasteful partly because of the actress. If a role like Lise was played by, say, Judy Garland, she would shower Jerry with indignant insults and glares. If she was played by Cyd Charisse, one would admire his guts. But when she's played by first-timer Leslie Caron she looks and acts like a shy, vulnerable teenager, and as a result Jerry just seems like a creep. And why DID they choose these other actors (though personally I'd rather they'd solved things by changing the lead) when the whole story hinges on the romance of these two young poor sweethearts disentangling themselves from their loveless commitments to older rich people? Not only is Gene Kelly a few years above Guetary and Foch, he's old enough to be Caron's father.
In short I think it all would have been improved by casting some young comedic-relief type dancer as Jerry, the kind that usually turned up in musical supporting roles...e.g. Ray MacDonald in GOOD NEWS or Bobby Van in SMALL TOWN GIRL. Maybe not them necessarily but someone LIKE them. Someone who could have chased Lise and made it seem harmlessly playful; someone who would have appeared genuinely happy living in that Chaplinesque hole-in-the-wall; someone whose humor and naivete would have contrasted better with Oscar Levant's sarcastic grumpiness. It probably also would have made the ballet seem less ponderous. And it might have provided a voice that could sing Gershwin better.
All this may give the impression that I don't like Gene Kelly. I do like him. He was terrific in most of his films, just not this one (well, and a few others). I don't despise AAIP itself, either; it has good points, like the art direction. And Leslie Caron, who despite her inexperience is rather charming, and really does look like she just stepped out of a painting. Georges Guetary does a fine job and his "Stairway to Paradise" is my favorite number in the movie. Nina Foch is beautiful and touching and should have ended up with SOMEBODY. But not Jerry Mulligan. I wouldn't wish that on her.