I love this show, I think it's even better than rome.
That said, the second season hasn't been as good as the first one so far because it is full of disappointments. Hard to believe Ragnar would disrespect lagertha like that and not care for her anymore, out of the blue. It's very far fetched. It's also unrealistic that the monk would want to stay with King Horik, who has zero consideration for him, rather than return with ragnar to scandinavia. Knowing full well that if captured he would be crucified? Not a very good move by the plot writers. Also the whole king Horik and floki thing is mostly unsubstantiated and out of the blue.
It's historically very accurate as far as my knowledge goes. I only wish they would focus more on the boats and the sea crossings, after the first one they didn't pay it any attention but it is one of the most interesting parts to me.
Also, in reality those big raids involved thousand of men. On the first raid there was only one boat, but now in the last one a shot shows more than 10 boats crossing the sea. And there's still only a handful of vikings? It's like they are short on cash to pay extras, but they need a LOT more if they want to portray big raid parties.
And they are making it seem like the raids only happened every couple of years and were big events. While the big organized raids were like that, it is my understanding that very often small raiding parties would go out and try to hit the weaker spots, like the north, hitting a monastery or something quickly and coming back with the treasures (like the first raid was). That's supposed to be happening all the time.
I like most of all the mushroom scenes, and the strong HPPD the monk is living with.