Repairs some faults from the first one and make Asgard looks a lot more realistic and Viking-like than a glossy set and the story expands a little on the established mythology. Chris Hemsworth has also grown good into the role and the ensemble do a solid job, but the inclusion of Loki feels forced and uninspired and most of the plot twists are easy to predict. The villain is also underwhelming. Some humor helps.
Much like the first "Thor" film, "The Dark World" has no shortage of visual splendor, from the amazing sets and costumes to the (mostly) impressive special effects. But, as with said first film, the spectacle can't overcome a bland and often confusing story, with way too many sudden tonal changes. When the film is over, you don't really feel that the franchise has made any significant progression.
It had its moments but the story is uneven and the big bad is frankly rubbish. The scenes with Loki half way in merely reinforce this. One of the first marvel films which felt like production line output, Alan Taylor undoes the good work he did on Game of Thrones and clearly could not shout loudly enough against the Marvel machine.