Thomas Picketty's account of wealth inequality in the United States and conclude that wealth inequality is closely tied to managing the relationship between the rate of return on capital and the rate of economic growth. Is the argument a good one? Does it have serious flaws? Is it overlooking something? Or is it plausible? There are lots of possibilities for critical engagement here. You could question the normative ideas in the argument, or you could challenge some aspect of Picketty's empirical discussion. The main thing to do is to take a clear stance about some aspect of the argument, dig in, and say something compelling about the aspect you've decided to focus on