I've never been a fan of whirlwind attack.
Also since it's a full round action you sacrifice the ability to put the boot into one guy and kill him (therefore getting hit less later...etc).
Once again, it's situational. If you're surrounded buthave flanking friends attacking more than one of your foes it's worth helping everyone out a bit untill you can see who needs the more help and who doesn't.
Both very valid points and for a figther with more feats than god it's not a problem to pick up a feat here or there that won't always be in use (By that i mean compared with say weapon focus).
Plus it used to be a prereq for the weaponmaster prestige class that completely disappeared in 3.5 to be replaced with a very different kind of weaponmaster that wasn't so broken
Onto another "broken" character class combination:
Rogue/Barbarian. There's nothing anywhere in the rules that says you can't sneak attack whilst raging. Go stealth berserker!
And to exagerate the point, try a halfling rogue/barbarian/blackguard. Now that really was broken.
The other way to go is the Dwarven, Rogue, Barbarian, Ranger
. So he's got flanking sneak attacks whenever he wants them, he goes berserk, dualwields and
gets ranger hatred bonuses against his racialy hated foes.
So basicaly he's a trollslayer
If you give him that tag team fighting feat it's nasty. That's the feat where you need multiple characters to have it but if they both flank the same creature they double the flanking bonus to +4. Now add in all the other bonuses and that's a pretty huge attack bonus (1 for ranger, 1 for dwarf, 4 for flanking + berserk stuff).
A much simpler "broken" character "build" is actualy the pregenerated fighter character from the Fighting Fantasy d20 adventures.
His feats look something like this:
Weapon Focus : Scimitar,
Weapon Specialisation: Scimitar,
Improved Critical: Scimitar
With his large strength of 18 and improved crit he has an obscene threat range and damage with that scimitar. He can also afford to take pretty hefty power attack bonuses (3 or 4 a round) and still almost garauntee a hit for d6+8 damage crit'ing on 15's.
Not bad for a 10th level fighter (before adding in any magic modifiers for magic equipment or spells). He seriously chews up monsters like nobody's business.