Well sure there are similarities, but as people have pointed out, everyone has inspiration. And you can have multiple flavours of the same things, i mean no one complains that one review magazine ripped off another (Writing a review on paper, who ever thought up such a thing!), so i see no reason to call Yahtzee a copycat for using the same medium and similar style. I'd also call him "fairly" original for developing his own style, which i've personally not really seen elsewhere.
But yeah at the end of the day, who cares? It's like ZOMG the PS3 copied the 360, which copied the Gamecube which copied the PSX which copied the SNES which copied the Megadrive which copied my calculator!!! Thus this proves my calculator is the ultimate gaming machine.
As for whether i actually accept Yahtzees opinion with him comedy. Yes and no.
It depends on the genre of game. I've always liked jRPGs and MMO's. He hates them both, and doesn't pretend otherwise. And him not liking it doesn't affect my enjoyment of the game at all, as he regularly points out, he tries to merit the game from the casual gamer point of view, and gives his own personal dislikes and likes. You then have to figure out if what you like coincides with what he likes. That said even if it doesn't, it doesn't necessarily matter, as the more Yahtzee tells me a jRPG is shit, the more i want to give it a go usually, as what he dislikes i like.
As long as you don't just require a "it's 8/10 buy! BUY! BUT EEETTT!", then you should be able to find his reviews helpful as well as funny in my opinion. If you are however the kind of person i mentioned above, you're probably not intelligent enough to get half the jokes he makes anyway.