I think it made sense to do it the way they did. In the books Half of why they set out was for Aragorn to reclaim the thrown. In the movies he doesn't want to be king.

What I would of changed is not have the elves come to helms deep, and instead have them come in ROTK when Elrond arrives with the sword. Theoden even said that they did not have enough riders, and that would of played off of the last alliance thing a lot better, then the elves coming to Helms deep which was stupid and made no sense.