I think that what you mean by 'legitimate' is that First Class had a pretence of seriousness that The Avengers lacked. But the fact that The Avengers embraced it's fun side was it's greatest strength. I guess it didn't come across as a sophisticated movie. It just focused on being a good one.
Exactly right. I can't stand when superhero films try to wedge in pseudo, half baked social or political commentary...XFC has so many moments where I just cringed because of the parallels they forced comparing it to gay rights, the most blatant being the line when Beast says "well you didn't ask, so I didn't tell." Cringe.
Not to mention all of the "mutant and proud" stuff...yes, there are parallels between mutants and gay rights, but they hit you over the head in the film pushing that message. Just be a comic book movie, please. Avengers was finally the first comicbook film I have ever seen, not a movie which is based on comicbook characters. It's one of my big complaints about TDK, the god awful cell phone part, which is thinly veiled commentary on the Bush administration and the PATRIOT Act, which the pretentious Nolans had to put in there, and I know something similar will be in TDKR.
Yes, there are parallels that can be drawn to current hot button social issues, but if you are going to do it just keep it very, very mild, and do it subtly. Superhero are powerful being who choose to wear silly costumes and save people. They are incredibly 2 dimensional characters, which isn't necessarily a bad thing. Don't try to make superheros something they aren't. Be an adventure film. Show heroism, show over the top evil villains, have some humor, some tragedy, even a love interest is fine. But stop trying to make it something it isn't, please. Just because a movie decides to tackle themes or issues that are deemed relevant to today's world does not make it good. A superhero film really should not be the place to make social commentary.