Although I disagree with your assessment of the other movies, it helped that the movie didn't have to get bogged down in origin stories. It just picks up where Thor and Captain America ended and assumes that anyone watching has either seen or heard of those movies.
As far as whether the movies were "good", I'm not sure you're giving the individual characters a fair shake. The Ang Lee Hulk went a little too deep into Bruce Banner's "abuse survivor" background, but The Incredible Hulk
corrected some of that and improved on the established relationship between Banner and Betty Ross. Admittedly, both movies were more whining self-recrimination than romping punch-fest, but the Hulk comics were always a littl whiney. Taken together, both Hulk films were the weakest of the bunch, but they served their purpos in expressing the origins and driving forces behind the character.
Thor was pretty much a reboot of the character. While keeping the basic elements of the character's origin, they dispensed with the Donald Blake alter ego (Thor uses Blake as an alias, but isn't actually trapped in the crippled doctor's body), but overall, the film stayed true to the character. Thor, in the film and the comic, is portrayed as a big dumb frat boy who means well, but often allows his temper and enthusiasm to overwhelm good sense (this is also the case in Avengers, but is subsumed by the battle between Captain America's sense of duty and Tony Stark's Ego).
Captain America did a lot with a very difficult subject. I actually came out of that film liking Cap and Steve Rogers a lot more than I went into it. Admittedly, the film was unabashedly nationalistic, but Cap was, in the 40's unabashedly nationalistic (remembering that, at the time, people from the United States had no issues with saying "America" and meaning only that part between the Rio Grande and the 42nd Parallel).
Captain America, besides establishing the Cap character, also established the primary basis for the film (the reimagined cosmic cube as an inexhaustible energy source/dimensional gateway), and even, subtly, established the basis of a S.H.I.E.L.D. movie by introducing (admittedly, in offhand fashion) the Howling Commandos, all of whom later become SHIELD agents (and yes, Whedon's use of Cobie Smulders and the introduction of the Council in the Avengers film almost guarantee that there will be a SHIELD film...possibly following the plot of the early ninetie graphic novel).
So while a film's "goodness" is an entirely subjective measure, you can't really say that any of the films were unsuccessful, since they all pretty much fulfilled their purpose of being entertaining while re-establishing well-loved and -known characters for a widely disparate audience.
What I lack in sincerity, I make up for in sarcasm.