Unjustly is the best way to describe the circumstances of his death because Kain didn't do anything to deserve that. (or did he?)
It doesn't matter now, now you're a
Vampire and you're back for revenge, the funny thing is your quest for revenge eventually is overshadowed first by Kain's moral dilemma of becoming a monster and second by him eventually becoming that monster.
im no expert on the franchise but in later Legacy of Kain games Kain is portayed as one of the oldest and stongest vampires and if not mistaken he is viewed as a Vampire king.
What i remember most about this game was its dark overtones, you play in a gothic gloomy world as a vampire sucking the blood out of innocent ppl who's suffering is voice acted.
In the dungeons of this game there are voice acted prisoners who are chained to replenish your health and their tortured moans merge with the creepy atmospheric music this game has.