Originally Posted by Mjölnir
1. It wasn't for me since I don't know if Loki betraying Thor is much of a plot twist. That's what Loki does. The thing is how and when is he going to do it, and what will come of it? I find it's about the journey, just as it is with that the hero generally always wins at the end.
2. It establishes that Selvig has gone crazy. I don't know if every scene has to advance the plot though. The funeral didn't further the plot, but it's a scene I definitely want to see because it of course brings a lot of other things.
3. I think the story of this movie was already over so it's just setting up a cliffhanger. I see nothing wrong with that as it doesn't break anything nor have any character act against who he is. As for the dark elves I certainly wouldn't have minded more with them. I'm very interested in seeing the cut scene where Bor kills Malekith's family, for example. I still think they worked though, kind of like Vader and the Empire in A New Hope, but more could have been even better.
I think Loki betraying then not betraying Thor was supposed to be a plot twist, maybe when you watch it again you can make a note of what sound effects they use, is it dark and ominous? If so it means we're supposed to believe that Loki is backstabbing Thor. Either way, my immediate reaction was "Loki's not really backstabbing Thor".
I thought the funeral scene advanced the plot very much. It set up that we had the death of a very important character (not just in the abstract as in "she's Thor's mother"), the other tombs demonstrated that there were a lot of casualties. It builds tension as now we know that war is coming, it's like when Achilles has a funeral for his cousin in Troy. The funeral scene built up the world of Asgaard, it set up their culture. It's world building. You need to build a sense of place, and the funeral scene did so. In contrast, whereas Asgaard is a primary setting, Selvig is a tertiary character. He doesn't need to be built up, I'm pretty sure that he, Darcy's graduate student, and Jane's failed love interest could all be removed from this film.
I agree I'd be interested in seeing a director's cut of Thor 2. It might be a much better movie.