Just how good is the current All Black side? The Economist can be relied upon to hunt down a quantitative answer, so if you want to know the win/loss percentage against any tier one side versus the All Black (at a neutral ground) then you should take this article as your starting point. I say starting point because it links to an even more detailed stats website focused on rugby if you wish to lose the better part of next week to the subject. 

But if you want to know how the All Blacks got this way, especially when you want to see how it came to be from an outsider's perspective, then you should take in this long article which covers the game from a grass-roots training and development perspective.