Because I'm bored, I'm going to attempt explaining this film without having yet seen it and without having read the final book as of yet.
1. The cliffhanger "see you in the sequel" ending
Assuming the movie follows the book, the story will end with a promise of a sequel. This is because the story follows a very simple formula for trilogies. In the first piece, write a self-contained story that doesn't guarantee a sequel, but is open enough for one to happen. Next, have a story that has plenty of new characters, new locations, and moves the plot along to where it sets up the last part. The most simple example of this in action is the original trilogy of Star Wars.
2. Class warfare
The Hunger Games is about, very simply, class warfare. The poor dying for the rich's amusement. How you can get anything else from that I don't know, but that is is what it is about. Its not about hating liberals, its not about hating conservatives, its not about religion, its not even really about slavery (although, I can see where that one came from). It is about the rich and powerful becoming so disconnected with the poor and the poor simply accepting their fate rather than fighting it (at least, until the plot came along).
3. The Fashions
A spin off of the class warfare bit, the fashion difference between the poor and rich isn't just to designate good and bad. The reason the poor are dressed like that isn't to make you feel sorry for them, it is because that is either all they can afford to do or they simply don't have time to spend on being fashionable. The reason the rich dress like that is because they DO have the time to spend on it and rather than sitting around being bored, they instead decide to find their hobbies.