This is actually pretty rare in a shounen.
Usually, when starting a fight or meeting a new adversary, the typical protagonist is lagging behind at first, then he(she) is on the verge of destruction and despair and it seems that, really, this time, everyone is going to die, THEN he(she) gets a flash of inspiration and discovers a whole new and brilliant technique/sees his(her) nakama in great danger, and loses it, thus gaining super anger-related strength/lets some random philosophical principle resurface from the dephts of his(her) heart, and it gives him(her) peace of mind and the power to crush the villains, etc, etc.
HERE, the male lead is unbeatable from the start (pretty much godly, in fact) and each ennemy that comes at him (underestimating him, of course because that's a lot funnier!) miserably fails...
Well in its own way, it's quite refreshing. Sometimes it's good to just be the epic undisputed overlord.
Concerning the art, the plot, the (other) characters, and the rhythm, it's all nice, other reviewers have already sung the praises of all that, I agree about most of it.
And maybe it's also due to the outstanding efficiency of both the author (fast writing) and the scanlators (fast releases), but this is COMPLETELY ADDICTIVE, really.
(PS: I realized I may seem bitter in my description of typical shounen. Don't get me wrong! I love shounen. Not all are like that, and when they are, I love it! I was just exxagerating a bit to make my point. ^^)