These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Fridge Brilliance: In the fairy tale, Cinderella's salvation comes from dancing at a ball, so it makes perfect sense to have Mary be a dancer.
Likewise, the climax at the dance competition.
The Scrappy: Holy carp, Dominique. She is an Abusive Parent and a complete Jerk Ass, and she has absolutely no redeeming qualities whatsoever. It's a wonder how she managed to get away with her treatment of Mary before the events of the film.
Surprisingly Improved Sequel: It did much better with critics than A Cinderella Story, and ranked as January 2009's No. 1 TV film when it aired on ABC Family. It also won the 2010 Writers Guild of America Award for Children's script-long form or special, which says a lot considering the first film was nominated for a Razzie.
The fact that there is another sequel (that will also have a musical theme, and star Lucy Hale, who is known for looking like Selena) in the works supports this.
The Woobie: Admit it, you wanted to hug Mary at least once during this movie. The poor girl just can't catch a break. Seriously, the way her so called family treats her crosses into abusive territory.