Keen's full-range critique of neoclassical economics is contained in his book Debunking Economics. Keen presents a wide variety of critiques on neoclassical economic theory, and argues that they show neoclassical assumptions are fundamentally flawed. Keen claims that several neoclassical assumptions are empirically unsupported (that is, they are unsupported by observable and repeatable phenomena) nor are they desirable for society at large (that is, they do not necessarily produce either efficiency or equity for the majority). He argues that economists' overall conclusions are very sensitive to small changes in these assumptions.
Keen's book closes with a survey of various schools of heterodox economics, concluding "None of these is at present strong enough or complete enough to declare itself a contender for the title of ‘the’ economic theory of the 21st century." However, he argues that neoclassical economics is a degenerative research program, not generating new knowledge but growing a belt of protective auxiliary hypotheses to shield its core beliefs from critique. There is an accompanying web site which provides more detailed mathematical expositions.
Read more about this topic: Steve Keen