I found this film rather interesting. It's as cheesy and campy as it could be, acting is rather bad, poorly plotted and special effects are simply ridiculous. However, I got hooked by it. It is a top expression of exploitation cinema (I mean, here in Mexico this flick was named "La sexorcista") full of fake blood, male audience oriented soft core lesbianism and ludicrous dialogs that seem to be copied from a Siglo de Oro play (Spanish Renaisence Theatre).
If you like exploitation films, give this one a try. It has its "artistic" aspirations but, as the director might have, you will forget them rather quickly. Fun fact: Here in Mexico, actor Enrique Rocha has grown a respectable reputation as a prime soap opera actor. By the way, one thing that really impressed me in this one was the lighting. For a 70's Mexican movie it is incredibly well lit!