It's lovely -- the look is hands-down the best part of the movie, not just in special effect, but in costuming and cinematography. It has a lot of little touches to make it look like a film made in the late 30s, like a scene where a crowd of people are looking up, and suddenly point when they see something in the sky -- and the shot is of three different arms pointing in perfect synchronicity.
Predictably, the story is incoherent and varies between unlikely, unbelievable, and ridiculous. No effort is wasted trying to make the characters' behavior seem logical or reasonable. Sadly, I've gotten used to this in Hollywood fare, so I'd be willing to overlook this problem.
No, what really sinks the movie for me is the two main characters. The female protagonist, in particular, is unlikeable and annoying. The male protagonist is not much better. There's no tension in the movie for me, because I really didn't care what happened to either of these people by the end. Some of the minor characters are more appealing, but the film doesn't show enough of them to make up for the general unpleasantness of the two central characters. And it's not like they're even anti-heroes -- the audience is clearly meant to sympathize with these folks, apparently on the strength of good looks alone, I dunno.
It has some good moments, and some visuals that are worth seeing, but overall, a big disappointment. It wouldn't've taken much to make an enjoyable film out of this premise, but this doesn't succeed.