First of all, don't expect strict realism from this movie; it's more of a fantasy.
Once you accept that, I think it's really well done. There are a few sketchy and unexplained parts, such as how an app can grant a wish and erase the memory of Christmas from the entire world, but as I said, it's a fantasy. Lyndsy Fonseca, I think, was a great choice for this movie and I felt a great deal of sympathy and affinity for her character. When she first meets up with her romantic interest (Hunter), you can tell he is quite taken by her. And I can understand why.
I was impressed with the merging of color and black-and-white portions in the scenes, and I think it added a great deal to the film. It was also interesting to see how the normally good-hearted characters could be so easily portrayed as not so pleasant with the change in circumstances, particularly the father. The ending could probably have been written a little better, but overall it was an enjoyable movie and I'd probably watch it again.