A film that, let's just say it, has not aged well. The plot, however faustian it may be, barely deserves to be called a plot. And you can hardly understand it, were it not for some title cards: I mean, there is no visual efficacity whatsoever. Some title-cards only, just a few ones: the others are quite impressionistic evocations of vague states of mind, sometimes merely a series of sigle words separated by full stops, and expressed in a sort of antiquated Italian language that not only nobody speaks today (believe me, I happen to be Italian), but into which not even the best literates of 1917 would have dared to write. (Of course nobody expects the best literates to have partecipated in the movie).
The worst weakness of the film, however, is the acting. In you are interested in the topic, by the by, I recommend you watch the movie until the end, if you can stand its about 45 minutes of growing bore. Well: never, not in a single moment we can find a "natural" body expression or gesture. (Though I'm pretty sure the filmmakers expressily didn't want to have any; I think that was a facet in the time's esthetics). But, for today's audiences, it's really hard to follow and appreciate a never-ending plethora of sterotyped gestures, with the protagonist Lyda Borelli flinging hes arms around like crazy from beginning to end, whether she is happy or sad, or Mephisto lurking from the bottom of the shot, in his heavy clownish make-up, to insinuate deadly temptation.