Keynesianism is seen as a failure because it was unable to characterize the problem (see MonthlyReviewSchool), never attained its goals and was never properly implemented by CorporateGovernment and the capitalist class. This lead to the phrase "Bastardized Keynesianism" as characterized by economists, arguing Keynes's ideas were never fully realized or accepted.
Considered a form of "third-way" or "lesser evil" politics and economics, Keynesianism is fundamentally an atempt to preserve capitalism.
The individual responsible for Keynesianism, John Maynard Keynes, is directly linked to developing New Deal Politics, the introduction of the Bretton Woods system, and the formation of the International Monetary Fund, World Bank, and Global Agreement on Tariffs and Trade (GATT).
See ImposedRationality, MixedEconomy?.
See also WikiPedia:Keynesianism and WikiPedia:Neo-Keynesian_Economics.