I haven't seen Atlas Shrugged Part 3 yet, but I will probably get it on Blu Ray.....
I was very disappointed that they moved the time frame up to NOW.....but I understand the budget reasons for it.....and then of course as MR BK mentioned, there are the cast changes.
And a key event was Dagny trading her diamond bracelet for a bracelet made of Reardon steel, and for some reason in the movie, it was a necklace that she traded.....no real reason for the change. Maybe they had a necklace in the prop room.