On the "not a scratch vs. instakill", I'm not sure where you've seen that, to be honest. Let's take a Mag 30+ of renegade militia with lasrifles. Lasguns deal 1D10+3, pen 0, which are increased to 3D10+3 by the horde's magnitude (the extra D10's cap at +2D10). On an average damage roll (20), your average space marine (TB8, 8 Armor points) takes 4 Wounds. Even a maximum damage hit will only deal 17 Wounds, which is less than the usual starting Wounds of a Space Marine. Meanwhile, if you're dealing with Guardsmen (or acolytes) as PC's, then why are you using Hordes anyway, and not single numbers of enemies?
Hordes are a bit of a problem. The number 1 issue is the fact they are boring, but their damage is probably the second most important issue. The idea is clearly that they are meant to chip away at the characters, but what they tended to do was "2 Damage, No Damage, 2 Damage, Oh, 28 Damage... erm, Critical Damage 5 on the head."
Lynata is actually right that most of the elements of Unnaturals could have been resolved by simply making other changes. Things with extra resilience could have had extra armour, or a note of extra toughness bonus. Things that hit harder could be noted as having a bonus to their damage (I am not convinced of using Natural Weapons as the way to do this, except for those that have inbuilt weapons, as it will not add to wielded weapons, but a note saying "This character adds +x damage too all melee attacks" would be sufficient). If you want to give a straight bonus to checks, then there is little reason not just to give a flat increase to the characteristic. Basically Unnatural Characteristics are a shorthand for doing all of the above, and due to the way they work have certain inflexibility to them. By splitting them up you can gain flexibility , which can also make it much easier to balance things properly. The only thing about Unnatural Attributes that isn't included in anything else is the "bonus degress of success in an opposed check", which 1) was the one that is most difficult to adjudicate on it's mechanical effect 2) there isn't anything stopping it being split into something else on its own.
Still not convinced it isn't a useful thing myself, but I can certainly see the arguments against it.
Edited by borithan