Both presidents' policies were largely dictated by necessity. President Roosevelt needed to establish an alliance with the USSR to help win the war. Once the war had been won, and with Russian boots on the ground in Eastern Europe, Roosevelt had little choice but to accept the harsh realities of the new political situation. Although critics railed against what they perceived as a sell-out at Yalta, in reality there was very little else that Roosevelt could have done under the circumstances. The Soviet Union was an atomic power, and as such direct armed confrontation between the two superpowers was unthinkable.

Truman understood this, which is why he adopted the strategy of containment to deal with the growing Soviet threat. Soviet domination of Eastern Europe couldn't be challenged directly, but the spread of Communism could nonetheless be contained—hence the implementation of practical steps by the Truman administration, such as the Marshall Plan. Truman's Soviet policy was perhaps bolder and more imaginative than Roosevelt's, but that was mainly because it had to be.

By the time the Cold War was heating up FDR was already very sick and his head was not really in the game.  He understood most of what the Soviets were about and how to deal with them diplomatically, but by the time the Yalta Conference took place he just wasn't himself anymore.  Truman was kind of clumsy in my opinion, at least in the beginning at Potsdam when he gave away our nuclear secret without any need to do so, or any reward or advantage for doing so.

He learned quickly though, and after Greece and Turkey and Kennan's Long Telegram, he reacted with a policy of containment at Berlin and elsewhere that was ultimately successful.

I don't think you can really criticize either man's policy.  They were both right for their time.

During World War II, it would have been crazy for FDR to treat the Soviet Union like an enemy.  Germany was clearly a major threat to the world order and the Soviets were a hugely useful ally.  I suppose you could say he gave them too much at Yalta, for example, but we really needed them against Germany.

Truman was surely right to start trying to contain the Soviets.  After WWII ended, they were clearly going to be an enemy and we could not have continued to treat them as if they were allies.