Well, at low levels moderate means "One might kill you if you're unlucky, more than one will probably kill you, several will summarilly slaughter you" if you're alone.
I'm not sure why this is, but in NWN there exists something I'd like to call "CR Inflation."
As levels go up, the CR of stuff thats the same level of challenge increases faster than levels.
Ex:
At very low levels a party is challenged by an equal number of easy creatures
At oh say 10ish +or- 4ish a party is challenged by an equal number of moderate creatures
At 20 a party is often fighting an equal number of very difficult creatures as a challenge
and so on and so on.
A party of level 30's or so will most of the time find themselves fighting things that are "impossible" pretty much constantly.
I could write about why this occurs for the next hour but I'll refrain from droning on and put forth a quick and dirty explanation:
1 - PCs become very versatile - A party prepared for what they're about to fight will be muuuch more effective. in a PW you're most often aware of what you're about to fight and can prepare accordingly.
2 - Monsters and NPCs become very versatile - BUT, they can't adapt. And the AI doesn't have the sophistication to use all their abilities in an effective way, even less, how to prepare and fight as a cohesive group maximizing their members strengths.
in other words, at higher levels the tactics you apply your abilities in become far more important than gross levels. This is because at higher levels you have more abilities, and so do monsters, but they dont use them well. So, at low levels, you're more on an even playing field with the monsters because there are fewer abilities on both sides that require intelligence to use effectively and thusly directly level gained features carry more weight (hp, ab) so level diferences mean more.
