Regarding the moon, did it shatter or did he move it with his punch or was this all in his own words?
Sentry and BM were around the same level of strength, its just BM got the the good punch in (they weren't overpowering each other like an adult to a child).
Agreed, he seem physically impressive and I don't think Skaar has time to amp his punch (the one that sent Hulk flying), but I wouldn't put down his Earth manipulation powers.
He was chatting with Uatu and got pissed because he was given the medal of freedom as a way to pacify him after he was basically told by president Kennedy to stop superheroing because he was black. A huge fissure spread out in either direction from the impact, and Uatu told him to dial it back, or he could split the moon. - http://imageshack.us/photo/my-image...can0004ui0.jpg/
And yeah, they were in the same strength league. But what made the punch impressive was that he got him with that punch after taking down the other Avengers. Including Ms. Marvel, Iron Man, and Wonderman. Then after getting divebombed from orbit, he got up and slugged it out with Sentry. Marvel fell first, but Sentry didn't stay standing too long after that, and he didn't fight anyone but Marvel.
And that 300 Trillion Ton Old Power Punch took waaaaay too long to charge, and while his earth powers are impressive, Marvel's got insane speed and energy powers on his side as well as outlandish strength. I see him wading through just about everything Skaar can bring to bear.
On top of those feats, the guy pushed an asteroid the size of the state of Arkansas off a collision course with Earth, as well as lifted a 93,000 ton aircraft carrier out of the water and flew it back to a base for repairs. No apparent effort on either part. Also took a Hydrogen Bomb exploding in his face with no problems and took down Anti-Man who walked all up and down the Avengers.
He BFR'd and flash ko'd him for a bit since he continued to fight the other Avengers while Sentry was unconscious. Then after divebombing him from orbit while he was fighting the other Avengers, BM fell over. With Sentry right behind him. The only reason Sentry stayed standing was because Ares and Wonderman held him up.
So to recap. Blue Marvel got jumped, beat up the Avengers, knocked Sentry out of the picture for a bit, then got sneak attacked while he was distracted. Then Sentry who was the person doing the sneak attack, couldn't even stay standing and needed assistance to stay standing up.