I've always remembered watching this one episode of Sailor Moon as a child, where Sailor Saturn is on the verge of destroying the world, and Sailor Moon, who knows that Sailor Saturn is innocent and isn't acting of her free will, refuses to kill her. At the time, my cousin and I were screaming at the TV saying, "WHAT ARE YOU DOING, JUST KILL HER ALREADY!!"
Of course, because it is Sailor Moon, everything works out in the end. But the question has never really left my mind: what is the right thing to do in that situation? And it's this exact question that has been plaguing my mind as I make my way through the final route of the fate/stay night VN.
Never would I have guessed that a story about mages summoning the spirits of mythological heroes to fight in a war for the Holy Grail would in reality be a philosophical exploration of the concept of a "hero." In particular, the heaven's feel route turns the story on its head and goes the furthest in questioning what is truly "the right thing to do" when a hero's personal interests clash with their larger responsibilities. In relation to the Sailor Moon example, the heaven's feel route essentially argues that, even though letting Sailor Saturn live was an illogical decision, it was a human decision, and one's responsibilities as a human being outweigh one's responsibilities as a hero.
That said, I think the idea that heaven's feel completely rejects the "superhero ideal" is a bit misguided. The VN itself is a little unclear on this matter. My understanding of it is, the true "superhero ideal" is Shirou's wish to save everybody, in every situation. In which case, Shirou's actions are consistent throughout all three routes. That was basically the major conflict in the UBW route, that Shirou ultimately refuses to compromise on this ideal (i.e. he refuses to sacrifice a minority to save the majority; no matter the odds, he wants to save everybody). The same is true in heaven's feel: when Shirou is forced to choose between saving Sakura or saving a greater number of people, he goes for option C--somehow saving everybody.
That is not to say that there is no difference between the three routes. UBW and heaven's feel in particular provide a more nuanced analysis of the concept of a hero, something that is noticeably and intentionally absent from the fate route. (Which is why I think it's a shame that the fate/stay night anime was adapted from the fate route, as a huge and vital chunk is missing from the "big picture.") What I take issue with is, a lot of people have the impression that heaven's feel is the "true route" of the game, and thus all the moralistic pandering throughout the first two routes can be completely ignored. But I think the ideas presented in heaven's feel are simply a piece of the puzzle, albeit a rather large piece.
My reading of the overall message of fate/stay night is:
While the "superhero ideal" is a good thing to strive for in general (fate route), when push comes to shove, the most important thing is for a person to protect the people they care about most (heaven's feel route). Failure to realize this will result in tragic, self-destructive "heroes" like Kiritsugu and Archer, and to a certain extent, Saber (UBW route).
Of course, this overly-simplifies things, but what I'm getting at is that heaven's feel simply stresses the need for a hero to change their priorities when the circumstances call for it. If a "hero" coldly sacrifices their loved ones simply because it is the most logical option, then they can no longer rightfully call themselves a hero, no matter how many people they ultimately end up saving. And worse yet, once a hero crosses that line, the damage is likely irreparable.
I find it funny that so many people lament that Shirou didn't turn out more like Kiritsugu, what with his dirty, underhanded tactics and his "badass old man" swag. But these people always fail to take note that, above all else, Kiritsugu was one miserable dude.
That said, Kiritsugu is my favorite master in fate/zero and Archer is my favorite character overall. I guess I'm weak for the tragic ones. xD