The biggest problem with Return of the Ape Man is the ape man. It looks like a modern guy in a cheap costume that could have been bought at a Halloween store. The make up is minimal and even by 1940's standards they had to have an idea of what a prehistoric man looked like...this isn't it! There's no change of posture, no over-sized brow. It's frustrating. The soundtrack is also very generic and could have been [and probably was] used for a number of other films containing action/adventure elements.
Still, Return of the Ape Man is not a total loss. The stars are worth watching just to see more of their body of work as actors. As long as your expectations are not too high, you might enjoy this one.
For more info check out the film's entry in IMDB.