Edit: Small creatures with reach weapons? Are there any except the heavy lance?
Something else: No 5ft steps anymore without AoO? IMHO a good idea.![]()
Well, it's even worse, now.
You have a Spiked Chain, and the Combat Reflexes, Hold the Line, and Karmic Strike feats. Your opponent is 3.5 Hasted.
He charges you, entering a threatened square (AoO - Hold the Line), then leaving a threatened square as he closes (AoO - movement). He throws a punch (AoO - unarmed attack) and hits (AoO - Karmic Strike). Then, with his Hasted attack, he punches again (AoO - unarmed attack) and hits (AoO - Karmic Strike).
If you can get six AoOs on someone who isn't unconscious, why can't you get six AoOs on someone who is?
And of course, the one-per-opportunity rule means that two people with high Dex and Combat Reflexes can get into the insanely-long disarm-provoke-disarm-provoke-disarm-provoke-disarm-counterdisarm-counterdisarm-counterdisarm-counterdisarm cycle that used to cap at one AoO each...
Bad ruling. Bad.
As far as unconcious individuals are concerned, they are not attacking or taking an action that provokes an attack of opportunity, thus you get no attacks of opportunity against them.
They are helpless enough that you can use your action to Coup De Gras them, which is much, much worse.
This is a bad ruling because some players will engage in abuse of the rules? Its up to the DM to arbitrate abusive use of the rules.
So how exactly does drinking a potion open more of a gap in someone's defences than standing frozen and unmoving?
Not necessarily - let's say you're using an axe. A full-round action to make a single x3 critical plus Fort Save...
... or six AoOs, most of which will hit, any of which might by themselves be a x3 critical... with a Full Attack on top?
How is it abusive to design a character whose fighting style involves taking advantages of openings left by his opponent?
An unconcious or held person is not engaged in combat, thus they do not leave their defences open against an attacker. They are not in combat. They are basically the equivalent of an inanimate object.
I would hope that most DM's would look upon moving in and out of a one threatened square as a single AOO.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.