Naked Capitalism has the post Is the Piketty Enthusiasm Bubble Subsiding? by Yves Smith. Yves has a lot of positive things to say about the book.  I think the following excerpt from her post is a good summary of what is troubling some critics of the Piketty book.

But as Taylor has pointed out in some technical detail, and others have alluded to, there are many reasons other than the invisible hand for r to remain high. Much of this can involve market failure, which Piketty explicitly rejects. See page 424 if you don’t believe me. R greater than g has nothing to do with market imperfections.

James Galbraith opened his review noting that capital meant power. If Piketty’s empirical analyses are right, and r has been persistently high, I’d suggest it reflects the power of the rich, not the natural forces of a free market economy. Higher taxes would help stymie the rich, but so would financial regulations, anti-trust campaigns, and public financing of politics that could minimize their power and privilege.

I’d like to read Piketty’s book with an open mind, but not an empty one.  That is why I wanted to make note of the criticisms.