Hal Jordan's Feats: The Power of the ring
According to Clark Kent AKA Superman, the power of the ring of Hal Jordan surpasses all quantification, it is infinite and the potential is staggering.
Now, remember that the ring alone is useless, it depends on the wielder in many ways, being the main ones the willpower of the wielder and the creativity - if he can imagine it, and he has enough willpower to do it, a Green Lantern Corps Power ring wielder can do anything and everything, emphasizing the can and not the will.
The power ring wielders usually have a strong sense of moral values and a right vs wrong compass.
God-level powers. Lantern corps were way powerful. Even though they're super powerful, they're limited by their numbers as to the amount of good they can do across the galaxy. There's always the chance of there being a parallax amongst them.