He lost on both fronts. 30 years later Hitler tried the same thing. He cruised into France, but failed to make any reasonable dent in Russia.
Is there something reasonably sophisticated about Russia that makes it difficult to invade?
Actually Germany during WWI was successful on the Eastern Front as Russia was dealing with economic instability and the Bolchevik seizure of power. Once the the Soviet government was established the Treaty of Brest-Litovsk was signed taking Russia out of WWI. Prior to the signing of the treaty German soldiers were getting closer to the Russian capital.
In 1914, the French were able to utilize their reserves to parry the German advance on the Marne. In 1940, the French strategic reserve, 7th Army, was sent to aid the Dutch, thus ensuring a weak screening force was left in the Ardennes, and when this was penetrated the bulk of France's Armies were trapped in Belgium. Even still, the Germans had to fight the French again for almost another month on the Weygand Line. Moreover, the communications, firepower and mobility of the German Army was far greater than in 1914, and there was also the presence of the Luftwaffe.
Germany and Austria-Hungary won in the east, but this was due to heavy Russian losses in tandem with failed economic mobilization, or at least organization, and a regime change. In WWII, the Red Army was far more formidable than the Tsarist Army, and the USSR more formidable than Tsarist Russia. Losses were heavy, but economic mobilization and organization, and strong centralized leadership were present. Combined with the USSR's strategic depth, and better organization of Allied aid, the USSR held on and was victorious.
The two things about Russia that makes it seemingly so hard to invade (The Germans weren't the only ones who tried unsuccessfully, think about Napoleon) are the immense size and the weather.
In warfare you are at an advantage if you fight defensively. You have the inner lines (shorter supply and reinforcement routes), also holding a position generally takes less men then attacking it.
Now with Russia's immense size supply lines for invading armies got huge. The Russians could retreat and the enemy had to push on, while their supply still had to come from the same source. So basically while the Russian supply lines got shorter the German got longer.
The harsh Russian winter is another thing. The Germans in WW II and the French were not properly prepared, also the weather made it close to impossible to advance. This is of course an advantage for the defending side, cause they have time to gather and reinforce their defences.
There are plenty of speculations about if Germany would have been succesfull if they invaded earlier. They might have taken Moscow then and force the Russians to give up. Of course there is no accurate way of proving this so it is rather unscientific.
/e btw : Hitler did not fight in France and Russia simultaneously. Until the invasion of Sicily there was only one front in Europe (not counting the air warfare. Which the Germans did count, as part of the 'Heimatfront')