How bad is it? It wastes talented actors and a chance to have social commentary.
Should you see it? Yes - it's hard to resist anything this idiotic in theme.
A racist surgeon, played by Ray Milland, is dying, so he has his head transplanted onto the shoulder of a convict being executed (Rosie Grier). The two heads bicker - and there's a funny scene as they punch each other in their faces - but any chance to say something about racism is squandered. Grier tries to clear himself of his murder charge, leading to ridiculous chase scenes, including a section on a motorcycle, where Milland's head is often replaced with an obvious dummy head. There's also a two-headed gorilla early in the film, but most of the laughs come from the ridiculousness of Ray Milland's entire body being poorly concealed behind Grier.