First playthrough vs later ones is pretty interesting. First playthrough I was almost exclusively lethal so when I got to the fight with The Sorrow and it brings out ghosts of everyone you killed I was like "oh holy shit I didn't think this would literally come back to haunt me!" Next playthrough I was as non-lethal as could be and it sure made that encounter a lot easier.

And that's nothing compared to how well MGS3 tackled this issue!