I find a couple of things interesting:

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If a top-flight macroeconomist, who knows the whole literature backwards and forwards, can so easily change his workhorse model in one year, and reverse all of his main predictions and policy prescriptions, then good for him, but it means that macroeconomics isn't producing a lot of reliable results.

Then again, New Keynesian models - and indeed, all of modern macro models - contain huge lists of equally unrealistic (and empirically falsifiable) assumptions about the behavior of economic agents.

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Models work good for some things. But what if underlying assumptions are wrong? How can correct answers come from a model with wrong assumptions? Can we really successfully "model" a complex economy?

John