I was really rooting for Haxan, really ready to like it, if only because "so I saw this awesome silent Swedish documentary on witchcraft"would be such a great way to start a conversation. Unfortunately, it hasn't aged well. Both the documentary and horror genres were in their infancy in the 20s, and Christensen isn't particularly prophetic on either front.
I love silent movies and think they're often unfairly criticized, but there's a lot to criticize here: the inconsistent acting, the occasionally ludicrous costumes, fact that nothing, literally nothing, happens for the first quarter-hour. The biggest problem is that no one on Haxan seems to have realized that what you don't see, or only think you see, is much scarier than what you do see. Every time Christensen fills his frame with cavorting demons and leering devils (and he's very fond of this) they get further from scary and closer to cute.
If you were a teenage boy in the 1920s, Haxan would have been a good way to see naked girls. Beyond that, it's hard to recommend.