The problem I have is you don't have many "Hero's" in video games. Sure, you have main characters, usually controlled by the player who face down impossible odds and yet somehow still manage to prevail, but that's not quite the same thing. Generally, in a video agme there is a certain inevitability to the engagement. The latest red faction demonstrates this marvelously - in spite of the obvious advantage in manpower and equipment, the EDF is clearly doomed to fail from the outset thanks to the inclusion of the player. Inevitably, mario, samus and link all fall prey to this exact problem - from the beginning you know with utter certainty that not only will they resolve the immediate threat, they will handily solve the entire dilemma and even neatly wrap the package on the way out. They are, in a word, super heroes, individuals who by their very nature tend to be the opposite of heroic. It takes no courage for Superman to foil a robbery - as he literally has nothing at stake but the brief time it takes to accomplish the task.
Gordon, while being the weakest character in the group (his characterization literally consists of "an early 30's man with a goatee and glasses, wearing a power armor analog who has but has never demonstrated a proficiency with advanced physics and mathematics" - everything else is the player's own creation), is the only one who strikes me as heroic. In the final accounting, he is not terribly well equipped to resolve the problems with any proficiency. His armor provides an edge, but in the end it's not much of one. His rudiemntary firearms training has been honed to perfection by a recent lifetime of firefights and near death experiences. But, at the end of it all, he is simply human. Gifted with neither the blessings of fate (like link) or with hyper advanced alien technology (like samus) nor any mystical abilitys to produce fire, change size or jump to astounding height (like mario), Gordon has been from the first game simply in over his head.
In the first game, halting the alien invasion was hardly a goal at all for the first 20 hours of the game - simply surviving was victory enough. Yet, when faced with the inevitable choice of continuing a desperate bid for escape or pursue a plan with so little hope for success that one could call it a fools hope, Gordon (or that is, the player) opts instead to plunge deep into the very heart of the nightmare. Samus does this because that is her job, link takes on the same challenges because that is his very purpose for existance and mario does this because that's how the mushroom kingdom works.
In the second game, the player is thurst into a world overrun by aliens resisted only by a fractured, weak movement who have no real hope of success. For the resistance in Half-Life 2 the only victory lay in dying a free man or woman. Yet, even when Gordon's arrival is heralded as nothing less than the second coming, when the entire world expects you to somehow play as savior to the universe you as a player are acting on the ineffable whims of an entity who doesn't even have a name. When you first step foot into the city, you, like the rest of humanity, likely see no course for victory and instead simply find yourself fighting with every ounce of power you possess to take another step forward. That we are not blessed with the certain forknowledge (and one cannot assume gordon is either) that victory will come in time makes the very act of defiance in the face of seemingly insurmountable odds heroic in and of itself.
Is gordon the best example of a hero in history - certainly not, but he's certainly among the best that video games have ever produced. By giving us an everyman for whom survival itself, let alone victory is uncertain, every act in the story becomes heroic. Heroism is, afterall, nothing more than chosing to continue on when hope is lost.