How bad is it? It's fairly typical Mexican horror, a bit worse than most.
Should you see it? If you're seeing all 4 films in the series.
Third of the four Aztec Mummy films, this one isn't the best, nor the most entertaining, nor the worst. The heroic mummy Papoca fights the superhero Angel and they both fight the evil Dr. Krupp. There's less plot, characterization and action than in the other films, which technically makes it pretty bad.