I also jumped on the one-punch-man bandwagon. it's been a while since I watched an anime...

first off: I feel that some scenes were much batter paced in the manga, mostly concerning the meteor and the robot, but also speed of sound sonic jumping around saitama. and that's it for mange comparisons.

I don't understand the need to ask about Saitama source of powers, it's akin to asking how can a cyborg exist given the current state of technology, how can the subterrean people live unnoticed in the bottom of the earth and how can a battle suit destroy a building without destroying the user as well. it's anime magic. but if you really want a 'semi-plausible' explanation - he got monster ooze inside his system when fighting the crab monster. EOF.

looking forward to watch the next episodes.