- A satisfactory ending. Not necessarily a happy one (see the original of The Little Mermaid for a clear example of a fairytale that didn't end what would usually be considered in a happy way). But the ending has to make sense and to suit the main character.
- A clear hero/heroine and villain. One of the things I love about fairytales is they do have a strong sense of right and wrong and strong characters on both sides of the "fence" are needed to achieve that.
- A little magic. But I also like characters to help themselves or prove themselves worthy of receiving magical help or, of course, both. Cinderella is a good example here. Clearly didn't deserve her ill-treatment but also a kindly soul despite it. So worthy of the fairy godmother's assistance? Definitely.
- A message without being preachy. A good fairytale will have a clear point to it and will not need to shout it out. It will become more and more obvious as the tale unfolds.
- The right character "winning". Usually this is the obvious hero/heroine but the Shrek films subverts this brilliantly by making the ogre the right character!
So who would be the right characters for your fairytales/magical stories and why? Are they really strong enough to carry your story?