The Russian invasion was a big fiasco. Well, mainly because of the weather. The Russian winter killed Hitler's troops as it did Nepoleon's years before. But the Russians had heavy casualties as well. The big difference was that the Russian troops were equipped to handle the weather. While the German troops were not. So in the end, the Russians just pushed on back to Germany. A short synopis I know. The only people who could successfully conquer Russia were the Monguls. They invaded from the east.
Well, in WWI the Germans successfully invaded Russia and it gave up, but then she had to surrender all that was gained with the Treaty of Brest-Litovsk. Russia was politically troubled, though, and you could argue that if the Russians had good, strong leadership and decent equipment they might have actually lasted until 1918.
As for Churchill, well he wasn't that important in the grand scheme of things, more a figurehead of Britain in WWII, who kept Britain in the war. But still, he's considered a wartime hero.