He was a humble and honorable one, a pretty down-to-earth hero that always had a smile in his face. Angeal did a fine job with him.
He just had bad luck and was killed because, even when facing an army by himself, he was willing to give his life to protect his friend. Without Zack there wouldn't be Cloud, and Sephiroth would have won. He wasn't the most powerful character in the world (even if he had the potential), but if what he did doesn't make him a true hero I don't know what would qualify as one.
And all that is also what makes Zack my fav FF character :)
