I am very much in line with Matt and Jess here. I especially like the idea of makign Power Attack and Combat Expertise in to standard combat maneuvers. Sure, it would get rid of the Fighting Defensively option, but who really needs that?
As a player, my favorite type of character is teh BDF. Over the years I have played shock trooper barbarians, half-orc clerics with the war domain (and Power Attack), half-orc two-weapon unarmed power attackers, etc. I don't play these character types because Power ATtack is a "broken" mechanic; I pick Power Attack as a feat because it is the only way to make a melee character feel like a contributor at high levels.
We've already seen the numbers on why Power Attack is useful (see the above example versus the Balor). A lot of people still seem to have the misconception that two-handed PA is overwhelmingly powerful compared to one-handed PA. Let me set that straight.
Gurt the 12th-level barbarian has 28 Strength while Greater Raging and he wields a +1 greataxe. Gurt deals 1d12+14 (9 STR * 1.5, +1 for magic weapon). If he manages to hit with all three attacks in a round, he deals 31d12+42.
Chukka the 12th-level half-orc Fighter uses Oversized Two-Weapon Fighting and has two +1 battle axes. He also has Greater TWF so he gets 6 attacks per round. We'll say he also has 1 level of barbarian (like any good fighter) and rages up to the same amount of Strength for a +28. He manages to land all 6 attacks (maybe they're fighting an ooze?) and deals 1d8+10 and 1d8+5 (off-hand), for a total of 6d8+45. So far, Chukka is ahead of Gurt for damage.
But wait, Gurt is a two-handed power attacker! He goes crazy against the ooze and blows all of his BAB, but since the ooze has AC 3 he still hits! Gurt rolls a Natural 20 on one of them, but is sad to find out that the ooze pays noa ttention to his critical hti. He still only deals his normal 2x Power Attack damage. Gurt now deals 3d12+42+72, or 3d12+114 damage. The ooze collapses in to a pool of... ooze.
Chukka attacks the same ooze. No, wait, Chukka attacks the other ooze, since Gurt just obliterated the first one. Even with Chukka's penalties for TWF, he throws in all of his BAB to power attack agains the AC 3 ooze and hits it 6 times. Chukka only gets a one-for-one damage bonus with his Power Attack, but he hits twice as many times so that makes up for the penalties. Chukka deals 6d8+48+72, or 6d8+120 damage. The ooze dies, but Gurt owes Chukka a drink because Chukka still ended up dealing more damaeg than Gurt.
Chukka and Gurt both gloat over the fact that they each kiled an ooze single-handedly and dealt well over 100 damage to it.
Meanwhile, Fud the Magician drops a 12d6 Cone of Cold on 4 creatures at once. They all fail their Reflex saves and none of them have ER, so they take 42 damage. Each. Fud may not have obliterated them in a single hit, but he did hefty damage to all of the critters and totaled 168 damage for the four of them.
Fud the Magician realizes he is a valuable contributor to the party even though his damage output against a single foe may not be as high as the Power Attackers of the group. He also knows that he has more tactical options when it coems to facing multiple enemies. Also, he can fly. What now, Chukka?
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Okay, the point is that Power Attack isn't the be-all/end-all of combat. The above examples are for ideal conditions; when an enemy has a fair AC the Power Attack mechanic requires a lot more tactical decision-making (as Matt and Jess have pointed out). Power Attack also doesn't exclude anyone who wishes to use it as a viable combat mechanic; chances are if you're not always getting two-for-one damage output, you're using other combat options that make your character viable and PA is just for some added effect, because 1d8+6 isn't a very exciting amount of damage at 18th level even if you DO get 6 or 7 attacks.
Finally, comparing Power Attacking fighters to Meteor Swarming Wizards is pointless. Sure, the BDF can put out a ton of damage each round, and sure, so can the Wizard. Maybe the Wizard can't Meteor Swarm indefinitely, but he can fly, polymorph, turn invisible, teleport, and Power Word: Kill. BDF can attack, attack, and attack. Why not let them be good at the one job they have?