[MENTION=26510] Sacrosanct[/MENTION] - you mention not accepting the criticism of "Mother May I" of earlier edition systems. Let me ask you a question. If I was playing a fighter and attacking an opponent in plate mail and I said, "I want to damage him in such a way that I do regular damage and damage his armour, reducing his AC by 2 for the rest of the fight" would you accept that? I'm thinking, and certainly my experience has been, that that would not fly at any 1e or 2e table. At a 3e table, it would be problematic since Sunder only applies to held weapons/shields. I suppose I could try to sunder a shield, but, then I'm not doing damage, and it only works on something that is carrying a shield. It's not what I'm trying to do. AFAIK, there aren't 3e rules for this.
In 4e, that's a simple 5th level Fighter Daily - Crack the Shell. Easy, peasy, over and done.
That's where the idea of Mother May I comes in. When the player has to negotiate with the DM to create effects and is entirely dependent on DM Fiat in order to actually perform the action. If the DM doesn't feel that it's appropriate (I slam my mace into the side of his plate mail, denting it and making it hard to move- deal weapon damage and -2 AC for the rest of the fight) then the player cannot attempt that action. And, in play, I find that most DM's are much more likely to say no than yes to players attempting things like this.
Do you think that my example would fly at most tables? That lacking a specific power structure like 4e, I could tell the DM that I was slamming my mace into the baddies' breast plate and denting it so that he takes a -2 AC penalty for the rest of the fight would fly?