David Harvey’s post on Piketty is available here. It adds to other reviews (see for example James K. Galbraith linked here; or Julio Juato’s here), very much in the same line, suggesting that while relevant from an empirical point of view, it is flawed from a theoretical perspective.
From his conclusion:

“There is much that is valuable in Piketty’s data sets. But his explanation as to why the inequalities and oligarchic tendencies arise is seriously flawed. His proposals as to the remedies for the inequalities are naïve if not utopian. And he has certainly not produced a working model for capital of the twenty-first century. For that we still need Marx or his modern-day equivalent.”