Just a few random thoughts:
You guys, when the people in LotR speak made up languages, those languages were actually crafted by a master linguist and took decades of effort. There's literature written in them, and they make sense. This does not mean that you need to make up a "language" every time you have some alien race in a movie. It was silly enough in the Hobbit where you actually had some grounds to do so; here it's just sad and adds absolutely nothing to the movie.
Major bonus points for one of the coolest and best designed end credit sequences I've seen in a long time. The post-credits scenes on the other hand were not necessarily a success - the first one at least is terrible, the second rather cute (on both counts).
The antagonist is indeed sorely lacking in depth, leaving it up to Loki to be both hero and antagonist. Which, fortunately, is precisely what made his Norse mythology inspiration the brilliant and memorable character that he is. In the end writing Loki's character and plotline well and having Tom Hiddleston to play him pretty much gave the director a free pass to mess up everything else and still come out ahead - all the other things done right are just icing on the cake.