I've always thought that having a fixed bonus and a fixed reduction in attack bonus would make a lot more sense. Plus, that would unify power attack with other feats that have fixed benefits and penalties. As well, I think that cleave should *require* the use of power attack.
An "aggressive attack" feat would be nice, too, where you lose AC in return for increasing your attack bonus.
The options and feats, below, would make combat against multiple opponents *much* more deadly, and would make combat reflexes a lot more useful. Using these options, I would allow a combatant to make attacks-of-opportunity using the same progression as with normal attacks. (At +6 BAB allowing an attack-of-opportunity at +6 and at +1.)
And, of course, all of this jiggering turns into just the beginning of a whole suite of changes, as one works through the impacts and rebalances combat.
(Ooh ... allow power attack on attacks-of-opportunity, but only allow cleave attacks on other attacks-of-opportunity, and over and above the normal count of attacks-of-opportunity that you are normally allowed.)
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So:
Power attack (Attack option): You may reduce your attack bonus by 4 in order to increase your damage by 2. You draw an attack-of-opportunity when you use this attack option. You may not use this option with a light weapon. With a two-handed weapon, your damage bonus is 4 instead of 2. You must use the power attack option to obtain the benefits of cleave.
Power attack (Feat): You may either reduce the penalty for using the power attack option to 2, or you may use the attack option without drawing an attack-of-opportunity.
Power specialization (Feat): You may obtain both benefits of the power attack feat. (Both the penalty reduction and the avoidance of an attack-of-opportunity).
Aggressive attack (Attack option): You may increase your attack bonus by 2 by reducing your armor class by 4. Using this attack option draws an attack-of-opportunity.
Aggressive attack (Feat): You may either reduce the penalty for using the aggressive attack option to 2, or you may use the attack option without drawing an attack-of-opportunity.
Aggression (Feat): You may obtain both benefits of the aggressive attack feat. (Both the penalty reduction and the avoidance of an attack-of-opportunity).
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(You may notice that I'm not a big fan of the feats that provide two bonuses, such as improved overrun, which provides both a +4 bonus and eliminates the attack-of-opportunity.)
