FF8 may be very fantasy but the characterization wasn't based on their histories for once. The cast members each had some sort of complex (or a few) that exist in the real world and that's what made them more 'real' characters than those of the previous FF games. A friend of mine
wrote a great post on the symbolism of this around 2001 if you like...
How the ensemble interacted and worked together in each new situation gave us a far more realistic example of the difficulties of working with different people. It may annoy players how each character seems to be diverting from what seems like the goal with their differences, because in previous FF games it was just follow the leader.
But I have to disagree on one point.. Squall's change wasn't as drastic as may initially seem and it was for the better.
Squall actually changed slowly through the course of the game. You'd have to look closer at what he says and does because he was in denial just about all the time. This includes his own thoughts to himself, especially where he's constantly trying to rationalize things.
It only seems drastic because the moment he stops lying to himself, FMVs and tons of awkward romance talk gets shoved in your face and there's no going back to the 'old' Squall. In the midst of that we forget that Rinoa changed, too. She used to always need people close to her but she grew and accepted that she would have to be alone to save everyone else. By the end of the game, they both became more 'normal'.
This is similar to FF7's reveal. The pummeling of effects/awkward romancy cutscenes in FF7's lifestream sequence and Highwind sequence may seem like a drastic turnaround for Cloud, but the hints of "it's not what it seemed" were already there.
So it may seem like Aerith would be who Cloud should end up with on a shallow surface level, but we know how that ended!