It has millions of fans, so it obviously must be a great Manga and Kishimoto must be a terrific writer - what kind of childish reasoning is this? People these days have no taste. Millions like content that is utterly garbage, let it be music, Movies, or even games. Mangas are no different. People these days like what entertains them, not what defines quality. Know the difference.
Sure, a lot of things in this manga carry great potential but Kishimoto is not a good writer in any sense of the word. His Deus Ex Machina device has been used and abused far too much for my liking. The blond lead character that carries the plot is one of the most poorly written characters I have ever come across - his convictions, his ideals ... everything screams mediocrity and redundancy with him.
Every time he opens his mouth, I find myself listening to the same blubber over and over and over again - it feels like a bad case of Rigor Mortis and his parents are just as poor - Kishimoto probably hit a perfect bad-writing lottery with these three. The political corruption behind the banal Will of Fire nonsense could have been handily exploited, but it seems that the author has virtually forgotten it all, lost it behind the plot that has possibly used all good versus evil cliches ever employed in the history of Literature. I cannot stress this enough.
His lack of skill is explicitly highlighted by the fact that he has created too many characters. It's a fact that no author can work around this many plots and do them justice. There is a limit to how many one can juggle. I cannot even name all of them he tried to put under the shade of depth and laughably failed.
If it wasn't for the metaphors behind Uchiha Clan and Sasuke, I would have given up on this manga a long time ago. Which is why I have chosen the last option, as Sasuke's descent to madness in MS form was the epitome of good writing. One needs to understand literature to fathom the depth of complexity behind his slip. Complexity and aesthetic sense, which all of NB probably lacks.