[From Cont'd] By changing Faramir's character slightly, making him more suspicious and power-hungry, Jackson has emphasized Faramir's troubled relationship with his brother and father as the black sheep of the Steward's family. He is anxious to do what is right for Gondor to the exclusion of all else because he wants to prove himself - he is only convinced otherwise when Sam compares him to Boromir. Naturally, his resentment for his favored brother comes to the surface at this point and he goes out of his way to prove that he is different. It makes sense, and it adds real tension in the Frodo storyline that is conspicuously absent in the encounter in the book. It's like Frodo's really been kidnapped. It reinforces the power of the Ring as a theme, and it introduces Faramir as an interesting and realistic character.
The second change is a little harder to justify because Frodo showing the Ring to a Nazgul is a dramatic departure from the book and seems to wreck havoc with the premise that Sauron doesn't know where the Ring is or who has it. Jackson added this sequence, though, because something needed to be added where Shelob would have gone at the end of Two Towers. The Frodo thread needed to be included in the climax somehow, but it had to be something smaller than Shelob to prevent Helm's Deep from being overshadowed. By inserting the confrontation with the Nazgul, Jackson makes a great impact with a brief sequence. The fell beasts are among the most striking visual images in the trilogy, and Jackson can bring one in to create an immediate impression in a brief scene. What should happen with the flying Nazgul, though? It should be obvious to everyone by now that Jackson places the "power of the Ring" theme at the forefront of the Frodo storyline, and this is another opportunity to show the Ring's effect on Frodo.
It's easy to trash this sequence just because it's cut from whole cloth, saying stuff like "an arrow wouldn't stop a fell beast" or "now Sauron knows that Frodo has the Ring and is taking it to Mt. Doom." It's just as easy to justify its plausability, though. What does Sauron now know? It's hard to say because of the Nazgul's altered perceptions, but it's safe to say he knew someone was standing there with the Ring. So Sauron knows that the Ring is at Osgiliath - this does NOT mean that he knows it's being taken to Mt. Doom. It is actually more likely that Sauron would assume the Ring is being wielded by the head of Osgiliath's Gondorian defenses, attempting to prevent the orcs from taking the city. This means that Gondor has the Ring and reinforces Sauron's motives for sending his amassed armies to Gondor.
Again, it's not a perfect fit, but Jackson was in a situation of having to serve the flow of the story by adding new material, and he did okay in my opinion. If anyone can think of a better brief mini-climax that could have been added to cap the Frodo thread in Two Towers with as great an impact as the confrontation with the fell beast, I'd love to hear it. Armchair Tolkien fans (arguably the only kind of Tolkien fan) seem to think they know more about script-writing than the three pros who wrote for the movie, but I don't think there's a fanboy in Christendom who would have written as watchable a script as the one we got from Jackson, Walsh, and Boyens.
