There is no denying the sheer power of these earliest Captain America stories. They are properly famous for their exquisite timing, presenting an attractive patriotic hero in pop culture at just the right historical moment when such a creation would resonate with maximum effect, but these stories are also quite compelling in their own right. Joe Simon and Jack Kirby kicked out yarns with oomph and savvy which were frankly just more exciting than those produced by many of their peers.
In Captain America Comics #1 we get a quartet of tales. One is the obligatory origin tale, not necessarily something all heroes of the Golden Age got, but Cap got a good one. Then the newly minted duo of Cap and Bucky go up against the saboteurs Omar and Sandu, a novelty stage mind reading act which covered Nazi action on the home front.
Then Cap takes on the weird and brutal Rathbone who uses chess to arrange his murders in support of the Nazi cause. And finally the duo face off against their most deadly nemesis, The Red Skull who is using a deadly list to murder important figures in the war cause. All of these stories have a weird darkness to them.
The doesn't go away in the second issue. A grim variation of the Yellow Peril shows up when Cap and Bucky must battle giant Oriential giants who it turns out are an enslaved tribe from the hidden recesses of the Himalayas.
They storm a Nazi stronghold giving Hitler himself heartburn. And finally they match wits with a deadly murderer who uses a wax museum as his lair. The impact of popular films was not lost on the Simon and Kirby team and they used many as templates for their own adventures.
In the third issue The Red Skull returns from the dead and this time uses a mammoth machine to dig through the Earth and demolish cities. He is routed of course by Cap and Bucky.
Then the duo go onto a movie set for the cause and run across a murder mystery which does a shout out to many an Errol Flynn epic. Finally in this issue they confront the Butterfly, a murderous predator despite his pretty name who lurks and plots in the shadows of a museum.
In the fourth issue Cap and Bucky confront a deadly mob of beggars who are dubbed "The Unholy Legion". This gang is also a bunch of Nazi saboteurs.
Then there's the strange and odd battle against Ivan the Terrible in which Cap and Bucky help Princess Betty Ross and her father the King against an usurper. This dream story owes no small amount to Hal Foster's fantastic Prince Valiant. Then the team battle counterfeiters who undermine the Allied cause and later they invade a deadly hospital which holds all sorts of deadly secrets and even a few monsters.
The fifth issue of Captain Ameica Comics pits Cap against the Ringmaster of Death and his fellow circus allies who are to a man Nazis. Then Cap and Bucky head to the Pacific and have to confront an enormous monster which turns out to be a wild and weird Japanese plot. The issue closes with the duo battling local Nazi sympathizers and taking a tour of a distant prison dubbed "Terror Island".
These stories are much more lurid than one might expect given the nature of of the hero Captain America, a hero for the battlefield. Cap and Bucky fight mostly against spies and saboteurs and often against merely greedy villains. What is a consistent theme is the sense of horror which permeates the atmosphere of most stories.