Okay, I feel like one of those people who go, "omg, the Glee cover was WAY better than the original", but...
I read Jean Giraudoux's Ondine when I was a child, and re-read it a thousand times since, plus I watched the wonderful comédie-française production, starring a young Isabelle Adjani, so it's fair to say I'm a little bit obsessed with Giraudoux's take on the story.
I guess since that story is practically set in stone in my mind, when I got to the original by Motte Fouqué, every page of it my brain would go, "No! That's not how it goes!"
...which is absurd because Giraudoux's work is an adaptation of this!
That being said, it's still a delightful fairytale, well worth reading (you can find it for free at Project Gutenberg!) And Arthur Rackham's illustrations are AMAZING! Look!
You can see all of his illustrations for this book at the site Rackham Fairy and Fairy Tale Art.