Existential Heroism: All or Nothing
For Camus, the Existential Hero is one who, like Sisyphus, grasped the absurd pointlessness of his task (existing) and chooses to embrace it anyway.  In many ways, this simply serves as a metaphor for our common fatal-fate: we cannot really appreciate what life is until we appreciate and accept death -- death, that thing that lays waste to our lives, erases their meaning -- you cannot be grateful for being alive only when you are happy but not when you are sad; you cannot, as it were, only love your family when they are kind to you.   Sisyphus overcomes his fate or doom by choosing a heroic attitude toward life's apparent meaninglessness; in this way he proves man can will meaning into any situation;  Sisyphus finds it in simply reforming his attitude toward his fate...something that eventually nearly all of us must do.

Thus, in Camus' The Plague the Catholic Priest, Father Paneloux realizes one cannot "honestly" or actually love God (or life, existence) unless one accepts that this God created a world of meaningless, terrible suffering; only the terror of the plague and witnessing children dying can teach the priest the true nature of charity and love and, thus, God. Put another way, if there is a God, He or it is the God of the Holocaust -- a god that allows evil and suffering to exist.  To love that God is to love that suffering -- this is the message of the Book Of Job:  as Satan tells God: untested faith is no faith at all, and it's easy for a rich, happy man to love you (or existence);  true faith is the love of suffering -- just as true love in a marriage or relationship is not loving the better, but the worse ("for better and for worse").  In this way Father Paneloux, like Sisyphus, rises above the meaninglessness of the plague: he embraces the entirety of creation in all its absurdity and pain.

Identically, in Man's Search For Meaning, Jewish Auschwitz survivor Viktor Frankl shows us that even in the most absurd, terrible, demeaning and powerless situations -- a concentration camp waiting to be condemned to death -- a man can still maintain or create his own human dignity and thus rise above his fate: "...everything can be taken from a man but one thing: the last of the human freedoms -- to choose one's attitude in any given set of circumstances, to choose one's own way" ... "in the final analysis it becomes clear that the sort of person the prisoner became was the result on an inner decision and not the result of camp influences alone."

In The Eternal Sunshine Of The Spotless Mind (also a great Postmodern film), the protagonist must finally choose whether he is willing to experience the pain of love.  If you knew how much love would hurt, would you still choose it?  If you knew all of your lover's problems before you dated her, would you still choose to date her?

The Existential Hero -- Sisyphus, Father Paneloux, Frankl -- all rise above life's meaninglessness by a) facing that meaninglessness face on (the rock, the plague, the prison camp = death) , b) accepting it, and b) creating meaning and virtue where there is none...knowing full well this meaning is fleeting and will not last eternally.

Achilles As The Original, Prototypical Existential Hero
Homer's The Iliad, centers around Achilles' recognition that:
a) If he stays to fight against Troy he will surely die, and to die is to forsake the most valuable thing he will ever have, the one and only life we are ever given (more valuable, he tells us, than hot slave chicks or riches and gold).

b) If he chooses not to fight, he can return home and live a happy life into old age.

c) This choice is entirely his own.  He is free to make it.  He alone must choose.

d) But such a choice will determine more than his life; it will determine the war itself (whether the Acheaens or Trojans win) and his legacy -- how he is remembered by others, or whether he actually is remembered by others: to return home is to live, yes, but to live without honor, and to die in battle is to die, but to die as a hero and thus to define himself as a hero. 

Unfortunately, perhaps like Hamlet, he chooses a bit late, reminding us that we are all condemned to choose, now. And so he learns, as we all do, that his choices also effect those he loves most.

Existential Hell, Existential Failure
In contrast, an "existential Hell", metaphorically speaking, is therefore a place where one is no longer free to choose one's own meaning. Existentialist failures are those who refuse to create their own meaning and instead blame others for their choices, paint themselves as "victims" of circumstance, and define themselves as others see them, rather than how they choose.  These are the themes treated in Sartre's play, No Exit.  Hell is not a place but a state of mind, one in which we do not accept and embrace responsibility for our own choices and accept our lives or circumstances as they are.

We can see Victor Frankenstein's Creature as an Existential failure -- or an Existential Monster -- because he allows others to define him, rather than defining himself or choosing a path that does not confirm the evil others associate with him:  he fails, and his failure leads to suffering, because he adopts others' perception of him -- as  monster -- as accurate.  In Sartre and Camus' philosophy, there is no room for this type of justification or escape from responsibility.  As Sartre says, "the alcoholic alone is responsible for his alcoholism" and cannot blame his childhood or genetics or fate etc.

Hamlet, and Hamlet, represent Existential tragedy; Hamlet is consumed by the larger Existential questions and unable to choose a course of action; he thinks, but he cannot act.  His failure to act eventually destroys not only himself but all those he loves. His obsession with seeking answers to the big questions allow his immediate fate to get the better of him: "to be or not to be"; "alas poor Yorick"; failure of choice; the meaninglessness of romantic love (his mother kills his father and marries his uncle): Hamlet Waxes Existential

Similarly, in Beckett's Waiting For Godot and Tom Stoppard's Rosencrantz and Guildenstern Are Dead the characters are caught in absurd hypothetical situations where they are  always waiting for meaning to arrive (in the shape of Godot = God) or they waste their time trying to answer to the question "what does it all mean?"

Rosencrantz and Guildenstern are, like Frankl and Sisyphus, caught in a situation they cannot act on or physically change: their fate is sealed because they are simply characters in a scripted play.  Because of this, they cannot define themselves as Frankl and Sisyphus do.  Logic and science do not help them answer the big questions, and yet they cannot help but ask them.  They're situation is absurd (they exist inside a play; it is not realism/realistic) and represents a Postmodern Existential comedy.  It's important to realize, though, that although their situation is absurd, hopeless, and eventually doomed, we learn much about our Existential questions by watching the play, or, from watching them play.  Their purpose is lost on them, but not on us.  They are Existential clowns in a Postmodern world.  But perhaps laughing at life's absurdity is itself the logical, heroic, rational response.

Thus, hell is despair itself (or perhaps clinical depression).  Hell is the failure to create meaning, to create moral or ethical values and then live in accord with them, or to confront the fact that others have created worlds that collide with ours and obliterate our attempts to live meaningfully.  Thus, hell is ourselves, or hell is other people.