I've been having an email debate with my brother over the merits of this trailer (he's not a huge fan, preferring the first one). He says that ending with Aragorn stumbling into Theoden's hall is a terrible way to end the trailer, it has way too much Liv Tyler, and it's clumsily structured to fit the framing sequence revolving around "hope."
After thinking about it, here's my thoughts on this subject.
SPOILERS AHEAD FOR ANYONE WHO HASN'T READ THE BOOKS ALTHOUGH IF THAT'S YOU THEN YOU PROBABLY DON'T READ THESE FORUMS.
The whole trailer hinges on Aragorn - it starts with Aragorn trying to bring the Fellowship back together and Aragorn finding out that Gandalf is back. Then it details the insurmountable odds he faces by showing what he is up against. Then it turns to Aragorn's tragic romance and a second, more realistic love interest for him to pursue, ending by highlighting the immensity of the conflict in a series of short clips and then a closing shot of Aragorn, obviously weary, making his dramatic entrance into the court of Theoden. The trailer highlights the importance of hope against difficult odds, and Aragorn IS hope - Gandalf tells him that the defenses must hold and he says, "They WILL hold." It's all about Aragorn stopping the forces of Saruman and Sauron from wiping men from the face of the earth. Those that believe in him (Arwen) believe that good will win, but those who have no faith in him (Elrond) believe that all is lost. I like that they play up the role of Aragorn as being the pivot point around which everything moves.
When Aragorn stumbles into the hall of Theoden, and you ask, "Is this man going to be able to stop two huge evil armies?" That's the question the trailer prompts, and with the movie's climax at Helm's Deep, it is the only large-scale question that this part of the trilogy will be able to solve. After Helm's Deep, Aragorn's ability to kick a** on a very large scale is no longer questioned. The trailer is designed to get you ready to see that.
My brother, however, doesn't buy this argument. He thinks that placing weight on the question of Aragorn fulfilling his heroic and royal potential is a mistake because it isn't in keeping with the themes of the book and doesn't bear itself out well in the first installment of the movies either. He pointed out the admittedly lame and forced exchange between Boromir and Aragorn at the Shards of Narsil in the first movie. However, I think that it makes sense to put Aragorn in the middle of things to make it personal and focused. If you widen the lens to emphasize the meeting of armies, it becomes too impersonal. If you shift emphasis to Frodo (where it really ought to be), the narrative drags because Frodo does very little in the second and third book. Is this a good enough excuse for placing the weight of the narrative on a fairly simple and undynamic character like Aragorn, trying to force him to be more than Tolkein intended for him to be?