From all the reviews and the clips I've seen, it appears they kept all of the plot lines, characters, scenes, and general dialog. However, the original dialog was dripping with Rand's objectivism philosophy to make a point, the movie mellowed that stuff out and replaced it with more subtle hints and used expressions and such to fill in some of the blanks.
Being such a huge book, it makes sense this is just part 1. They say this is the first third of the book, so maybe there will be three movies.