On the one hand, The Third Man has a great plot and some great performances and some great shiny-wet cobblestones in the Vienna night and a great ferris-wheel scene. Thanks, many commenters, for insisting that I see it next!
On the other hand, The Third Man has The. Most. Annoying. Zither. Soundtrack. Ever. Heavenly Ba’al, people, it’s your job to warn me about such things. What do you think the comment section is for? “Michael,” you’re supposed to say, “definitely check out The Third Man—but watch out for that maniac zither!!!” Please don’t let me down again.
I don't know that I'd go quite as far as Bérubé (or rather I would, except, thank goodness!, there are not very many zither sound tracks, so I'm going with the spirit of the claim), but I do admit that this is a sound track that I've never really understood.
Roger Ebert, however, writes this:
Has there ever been a film where the music more perfectly suited the action than in Carol Reed's "The Third Man"? The score was performed on a zither by Anton Karas, who was playing in a Vienna beerhouse one night when Reed heard him. The sound is jaunty but without joy, like whistling in the dark. It sets the tone; the action begins like an undergraduate lark and then reveals vicious undertones.
I might be convinced if Ebert fleshed out his interpretation, but I still find the zither irritatingly intrusive throughout the film, so any effective critical interpretation would, I think, have to account for that quality of the score. (Ebert does in fact hint at the beginning of such an interpretation with the idea that the sound of the zither "is jaunty but without joy.")