Ek Thi Daayan is not a horror film. At best, it's an attempt at a horror film, and a pretty good attempt at that. The good things about this movie, are Konkona Sen Sharma's acting and a few scary scenes that have been shot really well, so they manage to scare you.
As far as the story is concerned, I was not impressed. It could be either because I expected more from a movie that was made by Vishal Bhardwaj, or it could be simply because the story wasn't that great. Or maybe it's the association with Balaji Telefilms. I'm not too sure.