The first thing I want to say is that I did find the film enjoyable when I watched it, despite its flaws. I would even watch it again, with a friend who has not seen it. The visuals are creatively done and the film looks very nice, even though 3D will add NOTHING because it is not true 3D (filmed with 2 cameras) but the cheap converted kind. So, if you can, watch it in 2D.
The most important flaw is the story telling and some gaping plot holes. If you go see this, be aware that the story telling is clumsy at times and even though many topics are introduced, few of them are actually given time for a satisfying resolve. The second major flaw I found to be distracting were the transitions. They were done very badly and even took me out of the film sometimes.
Then, there is the romance. I understood from the first film, that Thor and Jane liked each other and fell in lust maybe, but they had known each other for what? 3 days? Now we are supposed to believe they are deeply in love, without anything to show us why. The relationship between Thor and Jane is a major focus of the film, so I am disappointed they wouldn't give it more time to develop.
Or more Loki. Seriously, for his prominence in the trailer(s) his scene count is rather slim.
The motives of our villain are NEVER elaborated upon. Seriously, all we know is that he wants to regain the Aether and bring darkness to the universe, without even telling us what that means, exactly. Are all the suns suddenly snuffed out, or what? Why does he want this? I assumed it was a metaphor for wiping out all other life, but it's NEVER EXPLAINED!
If you enjoy watching Chris Hemsworth, Natalie Portman and Tom Hiddleston without caring too much about the plot, if you enjoy creative visuals, a snarky Loki and some funny lines, go watch it. If not, you may be disappointed.
And by the way - the tag line to this film? Total bullshit. "He is forced to sacrifice everything to save us all." Thor sacrifices exactly nothing in this film.
During the battle in Vanaheim, they actually used guns. They have firearms and Asgard is STILL using melée weapons? Later in the film it is shown that Asgard also has artillery, which is NEVER explained. Seriously, what the fuck?!
Also, why can MEASUREMENT instruments be used to TELEPORT? How?
The ending with Loki as Odin was fucking awesome, though.