If you'd watched the first season of Shakugan no Shana, you'll be left wondering why the movie seems like an exact replica, as well as what appears to be a reused story plot from the last episode. To clear up the doubts, the movie IS what happened in the novels, while the episodes made altercations.
The first part of the movie is essentially a recap of the first few episodes of Season One. However, despite time constraints, characters like Yuji and Shana are fully developed, and we also get to see Fraigne the Hunter and Yukari in a new light.
The plot starts to deviate near the second half of the movie to great effect, turning the minor villain Fraigne into the real villain he is.
On the whole, the movie is a great refresher into the intro of Shakugan no Shana, as well as fleshing out an otherwise lack-luster Friagne.
Tip: Watch for out sneak appearances of Wilhemina within the movie. She appears 2 times. ;p