Saw this last night and while I was not expecting much I was very pleasantly surprised as this is a romp of a movie with great action, effects and laugh out loud humour!
Don't know much about the Avengers as I never read them, I'm more your Batman, Punisher and Wolverine type of hero (no powers or very little) and little team work (I know the X-men but what can you do!).
I don't want to give away much but Loki is back and he's got an army, the Avengers exist but only as a plan and on their own essentially and the superpowers element are not good playing with others at all (funny), there's a lot of tension and anger issues before we see cohesion and harmony.
Loki tears most of the team apart with his sneaky shenanigans and plans, The Hulk (best thing in the movie as the Hulk and Dr.Banner), Iron Man (second best thing) is his usual arrogant self, Thor does the shouting and the hammer work, Captain America is at first out of sorts but gels the team together, Black Widow has her work cut out and Hawkeye really grew on me, a lot of other faces from the other movies as well make appearances.
The action is brilliant, you really can't see the CGI if that makes sense, the humour is brilliant with the Hulk causing the most with his attitude to his own team not just the enemy, the ending is good and all in all a damn good watch!
Captain America says to the Hulk at one stage to get angry and the Hulk responds by saying that's his secret.........he's always ANGRY!!!!!
I also saw the movie in 2D deliberately!