I don't know how overlooked these are. When I was a kid they used to be on the Saturday morning cartoons, but I hadn't seen one in a while.
Eighteen of these cartoons were produced between 1941 and 1943. The cartoons were produced by Max Fleischer Studios (later Famous Studios) and were distributed by Paramount. The cast of radio's The Adventures of Superman supplied the voices for the cartoons: Bud Collyer, Joan Alexander, Jackson Beck, Julian Noa, and Jack Mercer.
Linked below is just over an hour's worth of Superman cartoons.
Superman: Volcano (1942)
Superman: The Mechanical Monsters (1941)
Superman: The Eleventh Hour (1942)
Superman: The Arctic Giant (1942)
Superman: Billion Dollar Limited (1942)
Superman: Jungle Drums (1943)
Superman: The Underground World (1943)