I think it's probably a consequence of my finding the term artsy to be rather silly in the first place. As I understand it, "artsy" generally seems to be used for films with an affected and noticeable style, and while that applies to Resnais' fiction films I don't see it in Night and Fog, though it has been years since I've seen it so perhaps I'm not remembering it correctly. I don't see what not being broadly seen has to do with something being "artsy." If that's what you mean then use obscure, though I wouldn't call Night and Fog obscure within the context of a film forum.