In the beginning, down-on-his-luck Morris is so depressed that he asks God why he is in the situation he is in. Then suddenly, Belofonte appears in his New York apartment. There is some funny banter between the two leads, especially when the angel claims to be Jewish and Mostel asks the angel if he is circumcised (Mostel's suspicions about Al being Jewish are later confirmed when he visits Al's predominantly African American synagogue). I thought the angel character would bring more lightheartedness to the situation Morris and his wife are in, but the film just gets more dark and depressing, and there's an eerie, ghostly sounding musical theme played throughout the film. It turns out that the angel is filled with less hope than Morris, and without giving away too much, the last scenes in the film felt somewhat bleak, certainly not Capra-esque.
I'd say it's worth seeing, but it's a tad bit bizarre. Good scenes of New York streets from the late 60s/ early 70s, and a terrific opening credit sequence. The great character actor Eli Wallach (who is to receive an Honorary Oscar this weekend) appears film for literally one second as a deli clerk in the beginning; if you blink you miss him (his wife Anne Jackson also appears in the deli; she's robbed by Al before he is killed and becomes an angel, we presume) For more about this film, here's a good review here at DVD Savant.