Instantly overpower the enemy, causing weapon damage. Only useable after the target dodges. The Overpower cannot be blocked, dodged or parried.
Overpower is a basic warrior counterattack. Once your opponent dodges an attack of yours, you have a chance to overpower. Overpower cannot be dodged/parried/blocked, but can miss. Overpower is instantaneous, so a high damage weapon is all that is needed here, not a high DPS weapon.
Overpower is a 5 Rage attack based on weapon damage with a 5 second cooldown. It instantly attacks the enemy for weapon damage. Rogues are especially vulnerable to it, as they rely on Dodge for much of their damage mitigation.
Works best with large Two-Handed Weapons. Most efficient warrior ability, damage per rage, so use it as often as you can.
Any warrior who uses Overpower often should consider the Arms talent Improved Overpower. It gives a bonus 25% crit chance for each of the two ranks, making a fully-Improved Overpower better than a 50/50 chance to crit. Combined with Deep Wounds and Impale, this gives an Overpower a great chance of landing a Critical which will deal weapon damage plus 100%(crit) plus 20%(Impale), and 48% in bleed damage(Deep Wounds), making it the equivalent of 2.6 swings.
The strategy is simple: If the enemy dodges, always use overpower. The only downsides are its limited use to Battle Stance, and while it can't be blocked, dodged, or parried, it can still miss.
Overpower can be devastating towards Rogues, so consider using Berserker Rage when fighting them to mitigate possible interruptions from Gouge.
Edit
Hotfix (2009-04-24): "[Glyph of Overpower] will now properly provide a 100% chance to enable Overpower after a parry." 
Patch 3.0.2 (2008-10-14): Overpower now only has one rank and no longer causes any bonus damage (i.e. weapon damage only). 
