After watching the Hatton fight, his mindnumbing speed is the difference. He's so fast he sends his opponents into a daze. With that speed comes power. He can hit hard, but his speed is the key.
Mostly Speed, followed by Power. similar to what advantage Roy Jones had over his opponents. The punches he lands that his opponents don't see hurts them the most.
SPEED. If you watch the first Marquez fight, it's not the power that gets him but the speed of Pac's hands. He hits Marquez a lot more flush and with a lot more power later in teh fight, but after he'd adjusted to Pac's speed he doesn't go down again. It's the punches you don't expect that hurt the most and that's what makes Pac special, not his raw power.
his speed and relentlessness....the ****er doesnt even look when he throws his power punches...his head completely drops and he's staring at the ground....
Handspeed and relentless aggression. Especially the handspeed, because of that Pac is able to exploit the holes in an opponent's defense so much easier, and with much deadlier effect.