These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Bucky Barnes. Generally speaking, until Ed Brubaker came up with own Alternative Character Interpretation of Bucky as a wetworks-type operative who killed so Captain America wouldn't have to, Bucky was seen as a joke character by many. Most writers portrayed him as a joke character, a parody of 40s era teen sidekicks or as an overtly pure soul whose death served as a major source of angst for Captain America.
Steve himself now unfortunately gets some of this due to Civil War and Avengers Vs. X-Men — is he really still the hero the world needs, or just an old man who's afraid of change and, perhaps even worse, a hypocrite who failed to stand up for a an underprivileged group - i.e., mutants - when they needed him? He's trying to atone for the last one after admitting that it's true — setting up Uncanny Avengers, a book focussing on a team made up of Avengers and X-Men, to help improve human/mutant relations.
Obviously the Civil War storyline is a major source of this for both Cap and Iron Man.
A more recent example cropped up when Bucky became Captain America and garnered a lot of popularity from fans, which led to the debate of whether Bucky was a better Cap than Steve Rogers himself, as well as whether he should have permanently kept the role.
Was Sharon's death in Captain America #10 a Heroic Sacrifice to save the world or a horrible fridging, the main purpose of which was to give Steve angst?
Rick Remender's run is already shaping up to be this. It's either a worthy successor to Ed Brubaker's work, or it's awful.
Johann Schmidt, better known as The Red Skull, is Arch-Enemy of Captain America and Bastard Understudy to Adolf Hitler himself. Once a bitter, psychotic street kid, Schmidt began as a petty criminal with a violent streak. After having his romantic advances rejected by a Jewish girl who'd been nice to him otherwise, Schmidt flew into a rage, killed her, and finding he liked murder, set out to commit it again. Convincing a friend to try and assassinate Hitler, Schmidt stepped in and saved Der Fuhrer's life. He then donned a Skull-shaped mask and took on the role of a grateful Hitler's spymaster. Trapped in suspended animation by Cap, Schmidt awakened in the modern era and resumed his old ways. Firmly convinced that Dystopia Justifies the Means and that everyone needs somebody to bully, Schmidt has committed every crime in the proverbial book, from the petty to the grandiose. He made several attempts at gaining World Domination through the use of the Cosmic Cube (killing thousands of people every time), attempted to transplant Adolf Hitler's brain into Captain America's body, tried to bodyjack Cap himself on several occasions, and fought The Kingpin for control of the New York drug trade. He has manipulated the Scarlet Witch as part of a plan to exterminate the world's mutant population, used his Dust of Death to gruesomely kill any subordinate who fails him or looks at him funny, and has been the mover and shaker behind countless Neo-Nazi movements, fascist governments, and terrorist cells, most notably Hydra and AIM. In a Bad Future he became God Emperor and spent his time triggering natural disasters, then showing up to inform people that he would not be saving them. When his daughter, Sin, was born, Schmidt planned to kill her for the crime of being a girl. While in a relationship with Mother Night, he brutalised her constantly. With an end goal of reducing society to its most primitive, dog-eat-dog levels, Schmidt is universally despised in both the superhero and supervillain communities.
Besides Skull, we have Arnim Zola, Mad Scientist extraordinaire. Zola was a Nazi biochemist in his human years. To escape mortality, Zola used his cybernetic brilliance to digitize himself and survive inside robotic shells to continue his experiments. One of his worst acts was to create the monstrous Hate-Monger, and afterwards he continued to complete multiple experiments for the Red Skull, his usual employer and master. Rick Remender however, shows that Zola was a monster just waiting to cut loose. When he and Captain America were lost in Dimension Z, Zola becomes its dictator, and its God. He inflicts horrible experiments amongst the people, overwriting their minds to be loyal to him alone and turns others into horrible mutants that he sics on those who don't accept his rule. Even his own children there are nothing but pawns, his affection to them fake to manipulate them and he is more than willing to kill them if they do not conform to his wishes. Zola, to end his long war with Captain America created a way to get back to Earth, with a bomb that would kill countless innocents before Zola sent his mutants, with the intent of overwriting the minds of the people of earth and mutating others, a process that would kill billions.
Pretty much any time Cap changes uniforms or codename, it will usually be seen as this by many fans.
We can't forget the brief period time where Cap was forced to wear a suit of armor after the Super-Soldier Serum was breaking down inside Cap's body and leaving him paralyzed. It was the 90s, after all.
Hilarious in Hindsight: In Annual #8 (1986) his team-up with Wolverine ends with Logan refusing to Save the Villain of the issue and letting him fall to near death. Disgusted Cap tells him that he will never let Wolverine into The Avengers. Fast forward into 2005 - and guess who is his new teammate? To be fair, Wolverine was brought on board by Iron Man, while Captain America openly opined, after Operation Galactic Storm, about how he could be so judgemental about Wolverine not being Avengers material, when half the Avengers team basically executed the living computer of the Kree Empire.
In issue 332, when deciding whether to give up his title and costume, one of his negative thoughts is charging into battle wielding a machine gun. And then look at how Bucky's incarnation of Cap charges into battle...
Speaking of Bucky Cap, an old issue of What If... ended up foreshadowing him taking up Cap's mantle 31 years before it actually happened in the mainline Marvel Universe in 2008.
Cap's first reappearance (Which was actually the villain Acrobat) in 1963 before joining The Avengers had him teaming up with Johnny Storm. Both would later be played by Chris Evans.
Ho Yay: Steve Rogers/Tony Stark. In an alternate universe where Tony Stark was female, they even got married◊.
Steve and the Falcon also have a lot of moments together during the course of their long partnership (the book was retitled "Captain America and the Falcon" from 1971-1978, and there was another series by that name in 2004-2005).
Like You Would Really Do It: Following the Civil War fiasco Captain America was shot by a sniper in the employ of Red Skull. He died tragically and everyone grieved and Marvel insisted over and over that he was dead FOR REALLY REAL THIS TIME, YOU GUYS! No one believed them for a second. Even ignoring the established fact that Death Is Cheap in comic books in general, Cap had a movie set to come out in a year's time anyway, and they wouldn't let the death stick. Turns out the bullet Cap was shot with? It was actually a device that cause him to phase in and out of space and time. He got better after a short intermission. All hail the great god Status Quo, blessed is his name.
Helmut Zemo is a more traditional example, walking the line between outright villain and Well-Intentioned Extremist, while being an expert chessmaster and manipulator who can incorporate the schemes of others into his own.
Memetic Mutation: Captain America punching Hitler on the cover of his first comic has become synonymous with Cap's badassery.
Englehart, while he retconned 'The Falcon' into a pimp whose memories were rewritten by the Red Skull, he did start to give Steve Rogers some much needed character development and tension that broke him away from an unquestioning My Country, Right or Wrong attitude. Perhaps it all culminated with Steve telling a very angry Nick Fury, in the middle of a fight, 'Nick... I haven't gained forty years (of my youth)... I lost them!'
Gruenwald gets "My Daddy" points for realizing how bad Captain America's rogues gallery was and pretty much spending his first couple of years on the book introducing new villains to serve as bad guys for Captain America, essentially creating at last one for practically every ideology imaginable. In particular, he gave us the Serpent Society (a revamp of the old Serpent Squad) and Crossbones. He also created "The Captain" and the replacement Cap (later US Agent), one of the defining stories of Cap's character.
Brubaker, on the other hand, gets props for resurrecting Bucky Barnesnote one of three characters that have been said to never be resurrected. The other two? Uncle Ben and Jason Todd (who's since been resurrected, though...)., and turning him into a likable character, as well as a worthy successor to the Mighty Shield after Steve's supposed death.
Sometimes, this is due to how much Flanderization Ultimate Cap is going through at the time. Early on, Cap was pretty Fair for Its Day with just some old-school White Knighting and a bit of frustration with the more shallow aspects of modern culture thrown in. After Vol.2, most writers (and readers) just remember the "doesn't stand for France" line (something Cap says he isn't even sure why he said that in the next issue) and build their entire interpretation of the character around that one line. So, now Cap irrationally hates the French and is a Grumpy Old Man with a bit of Values Dissonance thrown in. Even original writer Mark Millar does it now.
Also found in Steve Rogers relationship with Sharon Carter in Civil War. When they slept together, she was in the process of being mind controlled, and would later shoot him. She became pregnant and would later self-abort by stabbing herself in the stomach to keep the child from being used by Red Skull.
Also present to some degree in the fact that the personification of America leads a world-based team and is generally regarded as the best human in the world.
Captain America has gone rogue several times throughout his history to prove he isn't loyal to the government but to "the dream." Whether intentional or not, this always seems to happen whenever a Republican is President.
During the "replacement Cap" story of the 80's, Lemar Hoskins, the new Bucky, was black. What Mark Gruenwald didn't realize was that in some parts of the country, "buck" was used towards blacks as a slur. When several fans wrote in to tell him this, he pulled an Author's Saving Throw by having a character inform Lemar of this in a story, and also for good measure telling him that the first Bucky was a sidekick toward the first Cap, but he and the new Cap were equal partners, and he deserved a more dignified name. So Lemar changed his name to Battle Star (or Battlestar, depending on the source).
The Woobie / Iron Woobie: Bucky. Orphaned at a young age (and during The Great Depression to boot), lost his arm and his memory, used as an assassin by the KGB for sixty years, saw his best friend killed (he got better), tried for treason, and was acquitted only to be thrown into a Russian gulag.