Overall opinion: He saved capitalism by making liberal reforms
He wasn't a socialist. But he did enact into law some of the programs that socialists had been advocating for a long time. Like unemployment insurance, public rural electrification programs, and Social Security payments for retired people. Through the WPA and CCC programs the government directly hired millions of unemployed people.
The New Deal programs kept people from starving and possibly prevented a revolution, or possibly prevented a collapse into fascism. It saved capitalism.
He forced the rich to pay for everything. In 1942 he tried to set the top tax rate to 100%, setting a maximum income for the country. It didn't get past congress but they compromised and set the top tax rate to 94%.
He also did some horrible things, like all US presidents. Japanese internment comes to mind.
He also probably gave the best speech of any US president, this one:
This Republic had its beginning, and grew to its present strength, under the protection of certain inalienable political rights—among them the right of free speech, free press, free worship, trial by jury, freedom from unreasonable searches and seizures. They were our rights to life and liberty.
As our nation has grown in size and stature, however—as our industrial economy expanded—these political rights proved inadequate to assure us equality in the pursuit of happiness.
We have come to a clear realization of the fact that true individual freedom cannot exist without economic security and independence. “Necessitous men are not free men.”[3] People who are hungry and out of a job are the stuff of which dictatorships are made.
In our day these economic truths have become accepted as self-evident. We have accepted, so to speak, a second Bill of Rights under which a new basis of security and prosperity can be established for all—regardless of station, race, or creed.
Among these are:
The right to a useful and remunerative job in the industries or shops or farms or mines of the nation; The right to earn enough to provide adequate food and clothing and recreation; The right of every farmer to raise and sell his products at a return which will give him and his family a decent living; The right of every businessman, large and small, to trade in an atmosphere of freedom from unfair competition and domination by monopolies at home or abroad; The right of every family to a decent home; The right to adequate medical care and the opportunity to achieve and enjoy good health; The right to adequate protection from the economic fears of old age, sickness, accident, and unemployment; The right to a good education. All of these rights spell security. And after this war is won we must be prepared to move forward, in the implementation of these rights, to new goals of human happiness and well-being.