What Flotsom said pretty much sums it up. Not all though.
Hitler didn't really JUST want to win/capture the USSR, he wanted to DESTROY the red army. A planner like Guderian, would have had a different approach, which he did.
The attack plan included not just the goal, but also cooking up the enemy's armies to the point of destruction. Cauldron battle. Encircle the enemy and close in until the point of annihilation was the plan. So, blitzkrieg with a menace.
That is however much slower than simply carrying on and doing the job (tumble the enemy, capture the flag).
Then came the command of a southern swing, which kept the Germans busy both fighting and very much DRIVING before entering the issue of .... Moscow.
Moscow did not fall, but what cut that clear was within arty range. There was no grand battle of Moscow. The Germans had exhausted themselves with a combination (from command) of pointless battles, endless transport, complete waste of time, overstretched supply lines, too many enemies, and Hitler at the helm, making bull of the lot. (Thank you god). So they spent enough time while winter fell, and aided the Russians as "General Winter", which they were very much familiar with. By the way, the south of the line has to submit to winter one month later than Moscow.
Had the Germans gone straight for Moscow, done the job of USSR HQ, and then swung south for the feeding farms (Ukraine with the food, then the oil etc) they would have had the time. Had they had some access by sea, which was stopped by the British), they might have had even more success. And had they not been at war with the British in the first place, their force would have been quite much stronger.
So, they played a dicey game, and overstretched themselves to the limit where MAJOR mistakes could not work.