Most of the acting is decent enough in Mora Tau. However, Marjorie Eaton is terrible as Grandmother Peters. This role really needs to sizzle for this movie to work but Eaton is as stiff and wooden as the zombies onscreen.
The really bad news comes in the form of the "underwater" scenes which look like they were filmed by Ed Wood on a studio lot. Baaaaaaad. Furthermore, the zombies aren't menacing in the least and no one really explains how they got to be that way. The unspoken explanation has something to do with voodoo but then this theme is not explored in the movie at all. They just leave you hanging.
With a little more work this could have actually been a decent little zombie flick along the likes of Val Lewton's I Walked With a Zombie (1943) but it never quite gets there.
For more info check out the episode's entry in IMDB.