I skimmed a bit to avoid all the spoilers.
One quibble:
When Frodo, Sam, and Gollum reach the Black Gates Of Mordor they watch men who supposedly serve Sauron enter into the gates. This is obviously different from the book, and I cannot see why or how they fit in as of yet.
I confess I don't have my TTT copy with me at work, nor have I seen the movie yet. However: If I am not mistaken, Frodo and Sam do see some units of Easterlings arriving at the Morannon when they reach the Gate.