the qualities of a SOLIDER
Zack's mentor taught Zack not only how to fight, but how to fight with Dreams, Honor, and Pride three qualities he felt were essential to be successful as a SOLDIER. Despite that by the end of Crisis Core, Zack is the only one left who can still claim to still uphold all of these qualities. Zack was able to hold on to the principles instilled in him by his mentor, because he saw the consequences that all three generals faced when they lost sight of even one of these qualities.
Genesis, was the most ambitious of the generals. As a fan of heroics, happy endings, and fairy tales he ultimately placed his faith in Loveless, a play that told the story of friends who all lose something precious while seeking the "Gift of the Goddess". During his time at SOLDIER Genesis fought to surpass Sephiroth (eat apples with him) and become a hero, those were his dreams. Unfortunately the degradation that came as a result of Hollander's experiments squashed any hopes he may have had about those dreams coming true. For Genesis, the only hope he had left was in Loveless. He believed that by re-creating his favorite play, he would be able to receive the "Gift of the Goddess", a gift that he could never fully understand. In the end Genesis lost sight of his dreams when he felt his end was imminent and abandoned his friendships to fight alone. In addition however, Genesis also lost his pride. When he realized that he wasn't a normal human and on top of that, he was considered to be a failure. Genesis was no longer able to hold his head up as a proud member of SOLDIER. He abandoned Shinra to find a cure, and had to struggle and attack innocents just to survive. At the end of Crisis Core, he gains both his dreams and pride back after battling Zack. The damage was already done though, and Genesis lost his career, his friends, and his free will.
As the second of the three generals to fall, Angeal's most important loss was his pride. To Angeal pride meant everything. If Angeal couldn't believe that what he was, what he represented as a SOLDIER was the right thing, his position meant nothing. Therefore, Angeal's biggest fear was realized with the knowledge of his birth. Angeal believed the experiments performed on him made him a monster, and as a monster he was something that "causes the suffering of the world". Angeal could no longer take pride in himself or in the company that created him, which led him to suicide. He had Zack help kill him, thus ridding the world of a "monster". Angeal is never able to regain his own pride, however, it could be debated that Zack is Angeal's pride. Zack lived his life with honor and pride and was even able to fulfill his dreams. Though Zack, Angeal may have been able to regain some pride, not for himself, but for what he helped create.
Sephiroth was felled by his honor. He believed that he was truly doing what was right. He was a fan of fair fights and seeing Genesis and Angeal betray Shinra, and even worse, fight against him nearly breaks him. He couldn't understand why his friends would leave Shinra if there wasn't something going on beyond what he was told. His unease led him to consider leaving Shinra after the mission in Nibelheim. The events at Nibelheim shook him even further and led to his insanity. He couldn't accept that his entire existence was a lie, and in his madness he took it out on the town of Nibelheim. Sephiroth, though he never gained enough of his sanity back to realize it, had lost his honor. His honor was what made him the hero in the war against Wutai and what helped him to fight even against his best friends, and without it he was nothing. Sephiroth was never able to gain back his honor and from the looks of the series, he never will.
Unlike SOLDIER's finest, Zack is able to remain true to his ideals. By holding on to his dreams, his honor, and his pride, he was able to die as hero. He escaped Shinra, saved Cloud and without realizing it, saved the world. Zack never gained the glory one would expect a hero to get, but without a doubt he holds all the qualities of a hero. Without his pride as SOLDIER, which enabled him to keep moving on once his mentor left, his honor which helped him fight fairly even against the worst of odds, rescue Cloud, and save his life, and his dreams which kept him from giving up when the going got tough Zack would have never become a true hero and millions of fans wouldn't have had a game.