Captain America versus The Hulk and Superman: Why Does One Succeed Where the Others Fail?

From the title, you may presume I have seen Captain America: The Winter Soldier. Happily, the Young Man and I wandered into the cinema, leading to his family witnessing me squealing with joy over a film. I believe they are now aware of just how geeky I am. Fortunately, they don't seem to mind it.

Watching The Winter Soldier has led me to question how it is that Captain America has successfully carried off two solo films while the Hulk, Superman, and other superheroes, fail so miserably. I'm going to try to avoid any big spoilers, but just in case, here's a cut for the rest of this article.