Brilliant yet obscure; competent yet dilettantesque; visionary yet misguided... There is a lot to unpack in The General Theory.
I read the book and it is written with a heavy-handed jargon that freely mixes established economic terminology with Keynes's own innovations. I am firmly of the opinion that technical jargon and mathematical expression are important servants of economic analysis that should never be allowed to become masters. In Keynes's case, the consequence of the style is not clarity, but a needlessly frustrating reading experience.
Nonethless, the book also contains lucid sections and even a few inspiring and rhetorically powerful sections. This book is a real treasure trove of powerful quotations that distil important but counterintuitive ideas.
And speaking of counterintuitive, let me briefly talk about the contents (without any attempt to summarize the main arguments or to do justice to the pros and cons).
Aside from the obvious impact on trade cycle theory and depression management, the real strength of the book, in my opinion, is that it dares to go against the flow, to swim against the current, in so many crucial respects: 1) By positing a difference between the micro and the macro, and showing how the laws of the first need not operate on the second (and vice versa); 2) By denying the folk wisdom of "a penny saved is a penny earned" and the classical economic wisdom of household frugality (austerity) as a guide to sound fiscal policy under certain macro conditions. 3) By resuscitating numerous occasionally valuable heterodox theories, such as the theory of underconsumption (under the guise of aggregate demand management) and the Sentimentalist-Scottish-Mandevillean emphasis on the dark psychology of capitalism (under the guise of propensity to consume, animal spirits, etc). 4) And by mixing some fresh insights of psychology, probability theory, and complexity theory, with the classical insights of economics (although in a rudimentary way).
That said, there are severe problems with Keynes's theory - both in the pure formulation and in the impure application. The central notions of aggregate demand, the marginal efficiency of capital, the propensity to consume, full employment, the Kahn multiplier, etc., all seem to break down under careful scrutiny. The whole distinction between micro and macro might have been a big mistake. At the very least, the applicability of Keynesian concepts is much more tenuous and limited than might be supposed by the lofty title of a "General Theory."
But whatever the failings of the Keynesian enterprise (there goes one star!) and whatever the failings of the obscure prose (and there goes another!), the book is a rare achievement in two respects: in innovation and inspiration. It is impossible not to be delighted and impressed by the amount of valuable insights and out-of-the-box thinking contained herein.
The cute party trick of being a perennial contrarian seems less impressive when it leads to intellectual error and bad policy (both of which have been the occasional consequence of the General Theory). And the muddied terminology of Keynesian macroeconomics is a needless swamp. But the diversification and improvement of science - and social progress itself - is built upon the work of people who dare to be wrong in an enlightening way.
