What are some criticisms of Keynesian economics?

Keynes rose to prominence during the Great Depression, blaming the event on a lack of demand.The first point made by Keynes was that the appreciation in the real value of money (due to the gold standard) resulted in a dropping demand for goods.When there is a deflation rate of say, -25%, this means that the value of money will appreciate, relative to the goods and services you can buy, at a rate of 25%, so you will only make an investment (including expenditure) if the "interest" rate is at least 25%. This means that all transactions with an "interest" rate of less than 25% are never completed, and you are left with people putting their money under the mattress.Keynes's mistake, however, was to consider putting your money in a bank to be just as bad as putting your money under a mattress. The problem with his view is that when you don't have deflation, then saving your money (with interest) could very well be a rational choice in the long-run.This is not particularly hard to see: ultimately, both spending and investment can be represented as a growth in the value of your property -- for instance, the spending on your first light bulb might increase your productivity by 10x, thereby having an "interest" rate of 900% (obviously, when you spend on more light bulbs, the https://en.wikipedia.org/wiki/Marginal_utility decreases), and a bank might offer you an interest rate of say, 10%/annum. The richer you get, the less the marginal utility of goods and services you buy, and the interest rate you get at a bank becomes a better investment than buying another light bulb. This is a completely rational choice, and is the maximum growth of money you can achieve.When the government diverts this money into spending, it reduces economic growth, that is, the "Keynesian multiplier" is less than 1. Plain and simple.See for a more exhaustive critique. Also a new one: