First off, this is not the movie to watch when your wife is on the other side of the globe on a business trip, and you miss her.
That aside, there were two things I liked a great deal about this movie.
First, the color scheme. I probably get more excited than I should about color schemes in movies. But I really think this one works. It's almost all gray - all the hotel interiors are grey, Harrison Ford wears gray through the whole movie, a lot of the exteriors are shot with grays - concrete and macadam. And a lot of the outside scenes take place at gray times of day. Whatever isn't gray is usually a similar neutral color. I think Polanski likes to make noirs that don't observe that fundamental rule of noir: darkness. Chinatown was all golden afternoons; Frantic is all pearly dawns. Does it enhance the suspense? I think so. Frantic is about a man privately panicking, knowing something's wrong and unable to get anybody else to believe him. The cops, the hoteliers, the consulate - they're all unruffled. Imperturbable. Gray. It's almost as if the light itself doesn't believe him.
The other thing I like is the way it blurs the role of the femme fatale. The movie has two notable red presences: the protagonist's wife is wearing a red dress when she disappears. We don't even see her wearing it - we see her holding it, and know she's going to put it on, but we never see her in it until near the end. But all that time we have this image in mind of the doctor's wife in trouble somewhere, wearing a red dress. It becomes a sort of mental escape from all the gray - putting us somewhat in the place of the doctor, who just wants his wife back.
The other spot of red comes late in the movie when Michelle, the woman Ford's character finds who might be a clue to his wife's whereabouts, puts on a red dress to accompany him to a nightclub where... Anyway, by this time we've seen his wife in the red dress once, at the botched exchange. And now Michelle is in one. She's in the position of femme fatale in the film: young, sexy, doomed. She's a drug mule in way over her head; spies from two countries want her dead, and in following her around Ford's doctor is drawn deeper and deeper into the underworld. Standard femme fatale stuff, in other words. It's only cemented when she appears in the red dress.
But by this time in the film, the red dress has already come to mean something else for us: the doctor's wife. And that's when it hits you: the doctor has been running around with this Michelle for half the movie, he's been to her apartment, she's been to his room; he's told the French police that she's his mistress; he's even been naked in her bed. But there's no sexual tension between them. By design: we never for a moment feel that the doctor is in any danger of forgetting his wife.
It all comes together in a very interesting way in the end: both women are present at the final shootout, both dressed in red, and Ford tries to save both of them. Of course the femme fatale dies. There's this wondeful moment, though, when both the doctor and his wife are cradling the dying Michelle - both women in red are there, and there's no jealousy, no weirdness. Which is only right: she's young enough to be their daughter. But when was the last time you saw a movie obey that logic?