I thought it was good, it built off the first movie well, especially as it relates to the Thor and Loki dynamic that is the films driving force. It blends sci fi and fantasy really well with the mix being visually beautiful. Asgard is the stand out and I wish the film spent more time there with Thor showing Jane around.
The overarching story is a standard evil race want to take over the world (or Realms in this case) deal, but at the center of it is a great story of two brothers who are enemies bound by revenge and in Thor's case a quest to save his Lady love. Hemsworth and Hiddleston really bring this to life and the middle of the film with them together is when it's at it's best.
I also really liked the scenes with Odin and Thor that showcased how Thor has matured since the first film, it was kind of a role reversal. I'd have liked a bit more of The Warriors 3 but they do get a fun scene each. I liked the Thor and Jane dynamic again but as I mentioned above, more quiet time with them on Asgard would have been good.
I've seen quite a few mentions of the humour and I thought it mostly worked bar the 3 gags within the Thor vs Malekith fight.
The action is grander in scale than the first, the 2 big sequences on Asgard being especially good. Thor vs Kurse is a bit simple but I thought Thor vs Malekith was very imaginative.
The Dark World has some really great Loki moments that steal the film in my view, [BLACKOUT]the end shot being particularly great![/BLACKOUT]
It also features two fun cameos.
All in all a good addition to the MCU. 8/10