This was, for its time, a very influential and popular superhero comic. Of all the various superheroes that were depicted as socking Hitler in the jaw, Simon and Kirby's Captain America best exemplified the American propaganda effort to get the populace whipped up into an anti-Axis frenzy.
The book went through several changes throughout its run. Cap's teenaged sidekick, Bucky, was killed at one point - an occurrence that practically never happened within the medium, at least not at this time when comics were still a fairly young artform. The title even changed to Captain America's Weird Tales, briefly, with stories emphasizing more horror-oriented subjects, before being cancelled for a few years.
When the book returned (after being on hiatus between 1950 and 1954), Cap was a Commie-fighter, but the changes weren't any more successful, and it was cancelled again for good.