I agree with Soren, in that I think it makes sense for parry to be less effective for heavy armor users.
Heavy armor is more restrictive, so it would be harder to effectively parry, that's why armor check penalty exists. This ends up being a slight nerf to 2 handed users, but as was mentioned, 2 handers are still better off than they are in default nwn.
I understand your argument, Badelaire, that armor should reduce the damage you take from attacks. However! It actually does, just in an abstracted way. In dnd, armor's damage mitigating effects is represented by it's AC. When someone misses hitting a full-plate badass by 1-8 points, it doesn't mean that the fullplate warrior jumped out of the way like a ninja. It means that the person attacking them had a glancing blow across their armor, that wasn't effective enough to render any lasting damage or fatigue. Instead of reducing how much damage a person takes in an attack, dnd armor reduces the chance for a person to take any damage in an attack. In the same way HP is an abstract concept. When a person is at 1 hp, it doesn't mean that they have 4 arrows in their heart and are about to bleed out the next time someone sneezes on them. What being at low hp represents, is that your character is exhausted and all their luck is used up, so that the next time someone would successfully hit them, it's a telling blow. If you try to look at hp as being a non-abstract representation of your body, then the whole system gets kinda silly, and every adventurer would just be one giant walking scar.
(edit: This is also why your character is just as capable, combat wise, at 1 hp as they are at 100hp, btw)
As far as monks and parry, I feel like the power of the monk class isn't really an issue until high levels, so I'm not sure how much it matters. It might be better later on, yes, but it will still be quite mediocre early on, so it balances out.
All in all, this is a hardly noticable nerf to 2 handed fighters (1 ac never killed anyone
) and it makes light armor a lot more attractive, which is good, because dex based rangers and dex based fighters really need some help.
I say thumbs up.