I am an American.
I don't think the comic book character Captain America should be offensive to anyone.
Modern superhero comic books originated in the United States, and many took place during a time with high amounts of patriotism. Captain America is simply a product of that time.
Additionally, as a character, he is not over-the-top pro-American, but rather a figurehead unsure about his place in a world which no longer appeals to the values he was created to symbolize.
Other comic book characters were created with origins and close ties to nationality, and no one really complains. Numerous English heros, a few Japanese, hell even Wolverine is Canadian.
Honestly, anyone complaining about Captain America doesn't care about the character, culture, or people in America, but rather, dislikes some of the politcal actions of a few of America's politicians, and uses that as an excuse to whine about an entire country.