LOL, this is the problem with absolutism people like you. Nothing in this world is absolute. And not everything has justification for being liked.
The film was fun, the characters were interesting and everyone gets their share of action, audiences were entertained. Not every film has to have heavy plot to entertain people. The sense of camaraderie between the group was enough to provide the heart/memorable moments for the viewers.
I don't deny this (except the interesting characters bit the only interesting ones imo are Stark and Banner), but my point is for me to put Avengers on a high-tier it would've also had to have some emotional heaviness to it. Otherwise you don't feel anything. I didn't feel anything with Avengers.
Why does the action matter if there are no real stakes? If Loki wins I don't care. But I want Batman to beat Ras in BB because they spent half the movie building up development and giving you a reason to be on Batman's side. The only reason I'm on Avengers side is because Loki is absolute stereotypical boring villain with diabolical TAKE OVER THE WOOOORLD ambition and Downey is a funny guy. The charismatic nature of the Avengers is about the only thing holding that 'comradare' together.
Honestly the film would've been better if it was just Stark and Banner with fleshed out character stuff. They're the only people with chemistry and both of them becoming friends through their love of science/technology was cool. Put those 2 guys in a movie because they're the only ones worth watching.
Thor is not even a character I have no clue what he wants, why he does what he does, why he cares etc. and I've seen the Thor movie. You can't tell me he wants to break a sweat for for Natalie Portman the woman whom he had no chemistry or actual relationship with at all except 2 pretty people liking each other because they're 2 pretty people. Scarlett is nothing, the bow and arrow guy is nothing, Cap America has no reason to play nice with these people but he just does because he has nothing better to do. These characters are not interesting in the slightest. I liked Cap in the first half of his movie but I did not see that same valiant hero with a heart of gold in this one. Cap is just sort of thrown in there as the de facto leader but his new costume is goofy (old one looked awesome) and it's not believable to me that he can command authority over Stark's ego or a thunder god Thor.
Almost every scene in this movie I felt like I've seen before in some form or another just in the superhero genre alone (besides stuff like Hulk). I think you guys are raising your opinions too much based on eye candy and the fact that it wasn't a disaster as people were expecting. I'm telling you now I'm going to make a prediction: Dark Knight Rises will come out and nobody will be able to look back on Avengers the same way again (I'm no Nolan fanboy btw I shitted on Inception when people called that movie better than Matrix). You'll remember what it means to have a superhero movie that manages to balance both action and emotion and why it makes a movie so much better when you can do both (this is the reason Terminator 2 is god-tier of action films).