I have answered a similar question recently about New Deal policies, but the core of the question is whether or not Keynesian economics is better than Austerity. The idea is that the New Deal failed and that had the Roosevelt Administration just continued with the Hoover Era austerity measures the economy would have "self corrected." It really depends on your view of economics and how you view government intervention in the markets. Though historians like McElvaine ( a personal favorite) tend to side on the belief that the government needed to do something. Hoover's administration and the Republicans for the most part did very little, and there is a reason they lost the 1932 election in a landslide, and why Roosevelt and the Democrats would win the next 3 elections.

The New Deal was imperfect, but it did stabilize the economy during the 1930's. It may have not been a super success that brought the economy out of a slump instantaneously, but it stopped the free fall.