First at all, i am spanish, so maybe my english isn't good enough. I will try my best.
The bonus can be added or susbtracted, so a more skilled warrior could reduce the critical he has recieved. We only admit a maximum of +25 or -25 , but we never arrive so far normally if the foe is not surprised.
Well, we use it with every weapon. We don't feel any difference when engaged in pole arm situation, the example you give in spear and dagger has nothing to do with this rule. Dagger will only achieve A or B Criticals, and spear will achieve D or E if their OB is good enough. After this if the player with dagger is more skilled he will reduce the critical, but after recieving various bigger critical he will be wounded. What this rule does is reduce a bit the random rolls.
we had only changed two things: Projectile and hidden maneuvers.
About hidden maneuvers , ambush becomes really deadly, but let's be serious, if you manage to become near a foe by surprise armed (and knowing how to use the weapon) this guy has a lot of options about recieving a critical crit, and before it was frustating when after a succesful stalking you hit them in his feet.
So, hidden has to be reconsiderated, also invisible spells. We play invisibility as the movie "Predator", so if you move , you can be seen. Also in our games stalking is harder, so a 10th level thief not matter what his roll is will be hard time to be unnoticied by a 2th level guard at full day with anything to hide, regardless his Perception Skill. So Perception Vs Stalk has to be worked out; if you want to stalk someone you will have to do it as dark as possible, justify why you don't make sound, justify why the guard can't see you. Not the usual player saying: "I don't know how, i just have 100 bonus stalking" although the floor is noisy.
This has worked right in our games and is balanced... but now comes the unbalancing thing...HIDE. If you know when and where is going to pass someone you want to ambush, the ambush becomes really unbalanced. Stalking is hard, but wait for someone for example in a road with trees and HIDE, the victim will suffer a the first round of surprise. What happens? That bows and crosbows become more funny for players.
In the last years before this rule, players became bored about proyectile weapons, they always put a few ranks in some one, but they feel not very useful because there happens a lot that someone gets to them without time to change to melee. But now, everybody has proyectile, because with bows and hide you can add your skill ranks in bow and the victim don't. So people with 20 ranks, become a +20 to the crits, this make sure that at least the victim will be stunned one round.
But once again, it's true is unbalanced, but is the way people ambush in real world!!! Anyway we don't allow full ranks in you in a far range. So you can shoot with an OB modification due to far range, but don't have the Crits Rule.
Just a note, animal are considerated nos trained attacks, so they are away from this rule. And this has become a thing, that players are more afraid to fight boars, tigers and animals in general. In fact, it was like before this rule , but now they see this as a more random oppurtunity to get hurt.
So after this rule : People become more interested in planning attacks and having spells combinated like invisibility, no sound spells, ambush, bows etc. But hey, if the group combine their powers to make one player invisible, silent, good at stalking and good in a weapon...THEY ARE ROLEPLAYING AS GROUP!!
I am very happy about this House rule, i recommend to everyone.
Please ask any doubts you have, i will love to explain our experiencies and troubles with this House Rule.
PD: Note that the maximun +25 or -25 is for the difference about skill ranks. But we also add the ambush skill to this. So it will be the ranks with ambush plus the ranks in weapon that could become more that 25.
