(The following is something I wrote two years ago after the premiere of Captain America: Winter Soldier. And here we all find ourselves once more, now that Batman v Superman: Dawn of Justice and Captain America: Civil War have both premiered within the last month and a half. Anwhoo, I figured this might just still be applicable, and so I'm tossing it out there again. Ahem...)
It breaks down simply to one thing for me: Winter Soldier respected its title character, while the other did not; Captain America got to be Captain America, in a way that Superman was never allowed to.
Limitations & Struggle
Both of these characters are obviously limited, and are generally considered as boring, due to their strict moral code. But the fact remains that this strict moral code is what makes these characters who and what they are, and taking this away, for whatever reason, makes them into something they aren't. Man of Steel took the most moral of all super heroes and turned him into "SuperBro"; a guy who gets into catastrophic brawls in the middle of a city he's supposed to be protecting. He doesn't save Metropolis but rather actively participates in its destruction. Superman would never do this, under any circumstances, and that is the fundamental flaw of the entire movie.
The reason why Cap 2 works, on the other hand, is because the filmmakers didn't do this to Steve Rogers. They instead placed a man of his unwavering decency into an utterly foreign and incredibly challenging world (global espionage), thus making him have to deal with something uncomfortable and entirely outside his skill set. And he spends a great deal of time in the story struggling with this state of affairs, understandably so.
Struggle & Triumph
But then something happens: He fights his way through his exceedingly difficult circumstances by maintaining his sense of right and wrong and deciding for himself how the problem needs to be handled, relying on that sense to accomplish this. He finds his own noble path in this demonstrably un-noble world by refusing to compromise himself. And in so doing, he inspires those around him, like Black Widow and Nick Fury, to do the same. His very presence and example makes those near him into better people, which is the single greatest gift a hero can bestow on his world and the people who populate it.
And the second he gets done what he needs to — the moment he has succeeded in protecting innocent people and what he believes in — he stops fighting, and allows himself to be sacrificed, in more ways than one, for both his cause and his friend (i.e. in service to who and what he loves). Only, once again, his flawless example inspires yet another character, Bucky, to dig into himself and reconnect with his own humanity, saving both Rogers and probably himself in the process.
Triumph & Example
Those are the kinds of things that these kinds of characters need to do; it's what makes them who and what they are. Heroes like them aren't reckless, or aggressive, or impulsive; they never allow their situation to become about them and/or what they're doing first; they're servants of the greater good and don't let themselves forget it, no matter what.
Winter Soldier succeeded because it remembered this. Man of Steel failed because it did not.