How bad is it? It's actually the best of the Ator film series... but not good.
Should you see it? Yes, but not if you're hoping it'll be like the rest of the series.
I feel like I'm picking on Miles O'Keeffe, who's shown up often on this blog, especially as the actors who did later films in this series were worse. This time he has his hair braided and isn't wearing a loin cloth, but he does manage a lot of time standing around shirtless. This time, his twin brother (never mentioned otherwise) has become a metal skull-wearing bad guy that must be defeated. The film looks good: the location shooting is particularly good and the makeup is mostly okay (there's an annoying eyebrow, but I quibble). The soundtrack, probably recycled from another film, is also good.
There's still some campiness, but nothing like the D'Amato-filmed earlier Ator films.