Esther-Mirjam Sent on Sargent and more
Her concerns are more with the evolution of his thinking about rationality, from rational to bounded, which is a central pillar of neoclassical economics. She notes that Sargent's preoccupation with rationality (which should be contrasted with Simon's views) was to strengthen the theoretical foundations of neoclassical economics. I tend to be more concerned with the critique of those foundations, rather than with the question of how rational behavior leads (or not) to efficient market results.
One important area, in which I have done some research, is hyperinflation theory. Sargent basically is responsible for extending the Cagan model (his classic paper is here) and suggesting that beyond a monetary reform, a credible fiscal adjustment was essential for stabilization. In that sense, while Sargent maintained the fiscal fundamentals of hyperinflation, he suggested that expectations did have a role to play. As Carlos Bastos reminded me recently, here is a critique of Sargent's contribution published in the Economic Journal (subscription needed; portuguese version here). For an alternative discussion of inflation/hyperinflation go here, and for a survey of the literature here.
PS: Sent was one of the faculty members that left Notre Dame after the administration dismantled the heterodox program there. For more on that read here.