I think one reason this film is so maligned may be that many people did not know how to approach it. For instance, Letterboxd has one genre tag for this movie: “horror” — but, in practice, this aligns itself far more with the tradition of gothic romance—and/or also gothic romantic poetry—than that of horror (think Brontë, or even Keats or Byron, as opposed to Stoker, albeit all tied up with our contemporary conventions of “teenage girl” narratives). It is delicate, gentle, and oh so quietly, pensively foreboding with the occasional outburst of passion of course.
Another reason this might be maligned is for the possibly perceived silliness of its seriousness. But teenagers have a lot of confusions and worries and feelings and, yes, sometimes they’re silly, but in the moment they can feel so so important. This movie captures that.