I think Star Wars, Raiders and Jurassic Park are pretty much flawless films that changed the way people saw those kind of movies and the way they're made. I think The Avengers is a very fun movie, but I think it narratively is very clunky in its first act and when people are watching at home, they're going to not find it as endlessly entertaining as those movies. Also, a trick with those movies is the stakes are big. The raptors are scary. Darth Vader is awesome and menacing. The T-Rex getting out is freaky. The ark is very ominous throughout the movie. Loki and his aliens feel about as threatening as a villain from the Avengers cartoon series. Tom Hiddleston is great, but the menace isn't there.
I like The Avengers and it works because of Joss Whedon's amazing knack for writing characters and dialogue. He really makes the scenes of them bouncing off each other fun. But other than some questioning of government abuse of power without oversight at SHIELD with the cube that is glossed over, he doesn't really explore larger themes with his story like he has in Firefly, Serenity, Buffy, etc. Hopefully he can in the sequel. Because even in those other popcorn films you listed, you can see the question of scientific ethics in a very Frankenstein-context of man playing God in Jurassic Park, a question of religious belief and the fear of things beyond man's knowledge in Raiders and even the primordial conflict of a son grappling with both his father and the sins of the father in Star Wars.
Hopefully, Joss will be able to broaden the scope and raise the stakes in the sequel.