No real stars and no budget makes a B movie. In this case an excellent B movie.
The script is solid and confronts a real issue (though I don't believe the "over the fence" element). Maybe not stars but good actors like John Quaylen, Barbara Hale, Chester Morris, Jerry Paris, Johnny Johnston and the lead, Elroy Hirsh. Most people are interested in the movie because of the famous song. It is performed by Todd Duncan who also gives the movie's strongest performance. But I am certain most people except for true opera and theatre lovers know that Todd Duncan was the 1935 original lead in the stage production of "Porgy and Bess."