FDR was president through WW2. He demolished the norm of term limits and forced us to actually make it law. And he remade the country in his image. He's a great man, as in a Great Man of History. If you know your history and political and economic theory you can argue whether his New Deal (secured through bullying and slime, like any great politician) was good or bad, but don't let anyone make you feel bad for calling him a great president. Just accuse them of being a nazi and keep waving that flag.
That being said, it's fun seeing people have really strong opinions either way on him now, that was certainly true at the time. When you look at something like Grapes of Wrath, it's a great novel and an interesting view into the Dust Bowl and Great Depression, and it is also blatant, shameless pro-FDR and New Deal propaganda.
Edit: someone calling him a wheelchair-ridden fuck reminded me of this: Teddy Roosevelt overcame asthma; FDR was crippled by polio, and (more or less) successfully lied about it to the whole country. As in, it wasn't publicly acknowledged at the time, and he did stuff like practice supporting himself without the wheelchair between aides so that he could be seen "walking" publicly. Today he is celebrated as a differently-abled icon; back then he played down his being a cripple through force of will to sell himself to the American public (who, let's be real, still wouldn't vote for a cripple) to the tune of four terms.
Great man.