Coven lacked in mystery, while the viewer still wanted to know as much as possible about the circumstances the bigger and fearful basics were laid down pretty quickly.
In Murder House we didn't know what the heck was going on and therefore were presented with one part of the puzzle at the time, getting us closer and closer to the whole truth.
Asylum started to use this technique not as major portion anymore and instead gave the feeling of never knowing for certain what can be trusted, creating a very haunting atmosphere.
Coven couldn't deliver on such a level, I think that goes down to the nature of this horror story, which, well, focuses on witches, it’s the way we were introduced and told about this story, a rather open way. I don’t think this had necessarily to do with the story being more focused on a younger part of the cast, but maybe it didn’t feel as mature in theme because of that.
While I’m definitely not watching American Horror Story just to get scared, I still think this season also could have had the opportunity to set the point of view differently to present more surprises/reveal and a more frightening atmosphere. It's almost like the title intro showed more potential (in theme and tone) than the actual season, guess it's kind of ironic that the biggest mistake was to take away the magic surrounding the witches.
In general I still think that this season was awesome, but maybe not as good as the previous ones, it was a more enjoyable and pleasant season though.
Edit: Oh and for the for the record, my favorite season so far is Asylum, damn that one had it all. I'm not completely sure, but this season might still helped a lot for developing a better style of this series, the amount of different and significant recognizable shots should carry over.