It's worth noting that Piketty has an astonishingly basic misunderstanding/non-understanding of the marxist analysis of capitalism despite the titles of his books. He hasn't even read Capital. I like his politics relatively well as far as most liberals go but that is still pretty disappointing.

“What I mean,” Piketty says, explaining his differences with Marx, “is that your class position is not enough to determine your view of what’s the best system of property, education, taxation. We need ideas and ideologies and we need to take them seriously.” (Guardian in Feb). However, that is a trivially wrong mischaracterization. Marx himself was from a relatively privileged background and he, Engels, Lenin, etc have never argued for a mechanical determination of ideology.

In general I think his analysis is that "capitalism should just change some specific things to reduce inequality" without any materialist, political-economic understanding of why inequality is so rampant in the first place - why capital's dominance comes from the structure of the economy. That is why marxism is interesting, marxism makes a very compelling argument for it, and liberals ignore it at their peril.