The story has an original premise in that's it has a fairly familiar ideas (witches and magic - one of the oldest subjects for stories - strange kid moves into town and changes everything, secrets about the town are unveiled etc.) but the focus is on how the caster girl's powers affect her and her feelings of being outcast all her life, and the story revolves around a teen romance with a twist.
I went to see the film expecting to follow Lena, the caster girl who is struggling with the powers of light and dark inside her, but was (pleasantly) surprised to see the story was generally told from the point of view of her love interest Ethan, the 'normal' boy who falls for the outsider when everyone else shuns her. He's a very likable character, clearly passionate and compassionate, and has a good sense of humour that provides fresh light on the sometimes dark story matter.
It was also a bit creepier than I expected. There is conflict between the light and dark casters, as well as these elements within the characters, fighting for supremacy - danger and fear run through the film, and you will be surprised more than once.
Personally I found this film really entertaining, though I understand many fans are unhappy with the adaptation and I'm considering reading the books myself. I thought it offered everything, humour, action, fear, a sweet romance, a healthy dose of magic - and it's fresh! This is a solid, quality young adult movie.