It was fun.
The narrative itself is absolute garbage, but once you realize it is all just an excuse to get these fanboy service (self-service in Whedon's case) scenes on screen, you just sort of roll with it.
And those scenes are where this movie lives. Of course, if you're expecting any serious drama in these scenes, you've come to the wrong movie. Whedon makes no attempt to deviate from his 'let's lighten the mood' mentality, as he is having the characters crack jokes at every single turn.
You don't feel invested in the film in terms of caring about any of the stakes at hand, just as Whedon doesn't really seem invested in the story enough to come up with anything than the most convenient and ridiculous get out of jail free cards to bail out of each narrative conflict.
But like I said, it doesn't matter. You're there to watch these character banter with one another. And it's fun to watch. Like any comedy, I'm not sure how good it will be on rewatch once you know all the jokes, but there is some very satisfying humor and chemistry between the main players - good and bad, without spoiling anything.
The Avengers is Oceans 12 with ILM pumping a whole bunch of CG destruction into the background.
It sometimes loses it's focus and in typical Whedon style, gravitates toward less interesting side characters that are paper thin. There is one part that made me roll my eyes.
Lots of cheese. A lot of the bureau/SHIELD ops dialogue is just bad.
Hulk does absolutely own the film, though without spoiling anything, I will say that I was disappointed that Whedon seemed to contradict our introduction to The Hulk, as if he wasn't sure how to write around him without changing his character.
Action was very decent. I could see Paramount looking to Whedon for the next Transdongers after Bay.
I enjoyed it enough, but probably won't revisit until it hits TV, so that the jokes might hit again.
In the end, it's an ILM showcase with some nice comedy running throughout that doesn't take itself seriously. It's fun, but doesn't come anywhere near the top-tier superhero films.