My Top Ten List:

1. They turn Faramir into Boromir.  Faramir is supposed to represent what is good in the world and so rejects the ring which Boromir couldn't do. They even put Denethor's line, said to Faramir in the book, into Faramir's mouth. I will bring a mighty prize...

2a. Elrond doesn't respect Aragorn. In the book, he says that Aragorn can marry Arwen only if  he wins the war and becomes King. That seems fair but in the movie, he tells Aragorn that he can't marry Arwen under any circumstances.

2b. After his conversation with Elrond, Aragorn gives up on Arwen and tells her to go to the West. He even tells Eowyn that Arwen is gone already. That's great news for Eowyn!

3.  At the beginning of the battle for Helm's Deep, an army of elves arrives from Rivendell to help in the battle. What?!

4. Even though they have already cut out all the quiet bits of the story so that we can have only battles, they add an extra battle in which Aragorn falls off a cliff and is thought to be dead. What?!

5. Once Merry and Pippin have briefed Treebeard on what's happeing in the outside world, he convenes the Entmoot and they decide not to do anything. What?!

6. After Theoden has been rescued from Wormtongue and re-energized, we get a scene during the battle for Helm's Deep where Theoden gets cold feet and wants to run away. What?!

7. Gandalf is grinning as he kills Orcs.

8. After changing the whole story around and bringing Eowyn but not Eomer to Helm's Deep, Eowyn disappears during the entire battle.

9. They don't end The Two Towers at the right spot, i.e. "Frodo is alive but taken by the enemy." The end of both books are cliff hangers. But at the end of this movie, Frodo and Sam have yet to enter Shelob's lair. No cliffhanger...

10. At one point, even Frodo considers giving up and going home. No no no