Iron Man 3 spoiler/gripe:
Whatever happened to the 'Ten Rings' reference in the first film anyway?
And only ONE film has 'set the standard' and it's The Avengers.
It's implied that it was wiped out by the villain of Iron Man 1.
I kind of figured something tricky from Iron Man 3 when the director admitted he thought the Mandarin was stereotypical and cliche, if not racist. I kind of like what he did, but I hardcore comic fans didn't like it because it messed with status quo.
It was certainly better than the second one. As much as I like Micky R. I don't think the villain for that movie was really effectual. Honestly the whole series has had weak villains. :\
I don't know if I could in good conscious call the Avengers the standard because it's the product of so many more movies it's the sum total is greater than that of its parts, but it's crippled with each Marvel movie you don't see.
In fact, I was a little perplexed why Nazis were looking for Norse artifacts in Captain America, because I saw it before being able to see Thor.
Oh, and if Kenneth Branaugh doesn't direct Thor 2 I'm not watching it.
I'd say as a stand alone film the best standard there is would be Captain America.