Mantan Moreland really shines in this movie. He was a great character actor, and he had a LOT of screen time in King Of The Zombies. He wasn't a supporting character in King Of The Zombies; his part was equal among the main players and his name shared equal billing in the opening credits.
Forget what others say about racial stereotyping and enjoy his performance. The man worked with what he was given and took it to as much of a polished performance as possible. Blame Hollywood, not the actor, if you don't like his performance. His takes and reactions were superb. Smiley Burnette and Lou Costello did the same thing in "scary" situations, but Mantan Moreland had a flair for the comedy take that set him apart. He really was great on screen.
King Of The Zombies itself is not the best for a mystery/adventure movie from the time period, but it has the right feel for the time period if you like old movies. All the right elements are there for a fun movie. Why it doesn't really work better is a mystery. Don't expect too much and you will have a good time watching this one.