I was thinking about nether forces condemning the soul of an adventurer to eternal suffering - why not change it so that the outcome is alignment dependent?
Imagine dying as a chaotic character. The ghost would thereafter haunt *all* future PCs that encounter it, as chaotic creatures normally do.
A neutral character would after death have a chance to be non-hostile to neutrals (just a lost spirit roaming the dungeons) and could still be attacked by the PC if he wished that.
Finally, a lawful character dying would return as a ghost that does not attack other lawful creatures.
It wouldn't necessarily be lawful itself, as that usually prompts other monsters to attack it (vel blink dogs getting slaughtered after some time or occasional random ki-rins taking on deep CoC monsters on their own), but they would not attack a lawful PC.
This reflects at least some of their nature in the previous life and I think it makes sense that not all ghosts should be evil.