Here's the official poster.
The concept (and the costumes, which look like none-too-imaginative cosplay to me) just seem to continue the trend of an hour-long ad for Disney products, rather than be a unique spin on fairy tales or adding to the overall mythology of fairy tale villains.
Please don't misunderstand me: I would LOVE to be proven wrong and see brilliant and creative storytelling using fairy tale principles, and perhaps even drawing from actual fairy tales (even if they're put to use via the vehicle of these Disney-created characters). After all, I was pleasantly surprised to see the depiction of the Snow Queen in the "Frozen" half of this season. Her character and arc nuances (and Elizabeth Mitchell's acting - credit corrected 2-28-15) made the show worth watching, even though I cringed every time Anna and Elsa appeared in their straight-from-the-movie costumes like some weird sort of fan-fiction-slash-Disney-ad. (Note: I thought the actresses both did wonderfully in their given parts. They had the characterizations down extremely well, but there was just nothing subtle about the way they were written or shown. Instead it became like an hour long promo to grab the attention of Frozen fans when they were on screen. Not cool sorry!)
Once Upon A Time continues with the second half of season 4 on Sunday, March 1st.