When trailers and photos of the new film were released, die hard fans of the book were quick to find inconsistencies between the book and the movie. One example of this was how one of the new characters "Finnick" was portrayed in the trailer. Some felt that the actor is not a fit for the role and does not embody the character that they envisioned in the book. Although it is too early to tell if the movie will stay true to the book much like the first one did, fans are skeptical.
Another reason fans of the series are worried about the upcoming film is that some were disappointed in the book itself. The first book received all around better feedback than the second and third in the series, and some fans believe this will be reflected in the movie. These fans might even welcome film makers taking the liberty to change the story up a bit and add a little more action (which was the primary complaint of Catching Fire naysayers).
Whether through tweaking the story line or sticking to the script, Hunger Game fans can only hope that the movie interpretation of Catching Fire lives up to the reputation the first movie left for it. Personally, I feel that the book had enough action to work into an entertaining movie, but only time will tell. Be sure to see the movie, read the books, and form an opinion yourself!