My experience with playing Barbarians with "big mofo weapons" is that you want to Power Attack every round to a point where your second-last attack hits on a 3, or thereabouts (obviously relates to higher levels and tougher monsters). Against hard to hit, low-HP creatures (armoured humans!) Power Attack is a liability, so use it with care. I found going anywhere but top of the initiative order helpful, so I could gauge how tough the enemy was before leaping into battle. As such, I studiously avoided Improved Initiative.
Anything that gives you a bonus to hit means an extra point into Power Attack, which is an extra 2 damage per hit. Once you hit level 6, the full attack option is nearly twice as good as a standard attack. Until then, Cleave is your best friend for ploughing through hordes of mooks.
Bonuses to hit inclues extra strength bonuses. I would say straight Barbarian works well, and is simple to play into the bargain. The Greater Rage and Mighty Rage abilities are far better than standard Rage (gain of 3HP/level over 11 levels = 33HP), though many players don't realise this until they actually get to use the abilities. Stay as close to possible to the straight Barbarian path as you can. When you stray, keep to full-BAB classes. After level 6 I wouldn't Rage until you can make a full attack, unless you need the HP or last-gasp extra damage hit.
Now, you're taking an exotic weapon and you need the damage dealing feats as well (sounds also like you're a demihuman?). I would take Fighter at level 3, using your Fighter feat to pick up the weapon proficiency. Your other level 3 feat should be either cleave or weapon focus. Take a second level of fighter at level 4 (taking the choice you didn't take at level 3). Then stay Barbarian (Damage Resistance is awesome).
It's a simple setup and isn't optimised to the last iota. It is, however, versatile (doesn't need a horse/outdoor space), effective and easy to play. Specific weaknesses are terrain preventing a charge, flying enemies and Will saves. It combines well with other character's abilities (Clerics love casting Bull Strength on a guy with a strength of 20 already, just to see what happens).
