Oh, I know, right? The characters ARE teenagers, but, the tone of the books isn't necessarily teen. Sure, there's some teen angst amongst them, but Bella is mature for her 17 years. You're right about the mood, too; that's how I feel. I know the lines are going to be out of place, and that there are added scenes and deleted scenes; they can't put everything in the film. I feel that as long as the core components are there, I'll be happy!
Oh, and as far as the cast goes... I guess I'll put it here, since it concerns the whole cast. I'm rather glad that they didn't cast HUGE stars for this movie. Sure, there are some actors that are more well-known that others... I only recognized Rob, Kristin, Elizabeth, and Nikki. I had no clue who the others were! I feel they were right in doing this; I have no idea if more recognizable or popular stars auditioned for the roles... they don't usually publicize that. I think they did right by having a few bigger names- that's what caught my attention- they hook you with a name, hoping that will draw the audience in!! By having lesser-known actors in the movie I think lends a "real" quality to this fantasy world that we love!!