I think FDR was a "great" President, and I'm about as conservative as one can be. Under FDR and his leadership (in particular, his Lend-Lease), we became the superpower.
We became a superpower when Theodore Roosevelt sent our ships halfway around the world and swiped Spain's colonies. That's why our participation in WW1 was critical to bringing that conflict to a swifter resolution.
If FDR had been more interested in something other than spreading communism, WW 2 would have been unnecessary IMO.