I agree with the points made above regarding SU weakness and GER Strength although i counter it with the fact that SU did suffer hordes of losses because of poor doctrines and training but produced much faster.
SU suffered because of poor leadership and the purges, and to somewhat lesser extent, poorer training and lack of good equipment in the beginning.
USSR didn't have worse doctrine in reality. Actually, it was a world leader in mobile warfare in mid-30.
During the Russian civil war, Red Army fought not just the White Army but also had to fight off Polish invasion and several intervention forces than landed in Russia - Brits and Americans in Archangels and Murmansk, French in Crimea and Caucasus, Czech veterans that took control of Trans-Siberian railroad and cut off Russian Far East where Japanese and Americans roamed at will. Red Army was outnumbered and had to cover vast amounts of land. That war was much more mobile than the one in the west. Red Army had to end the battles quickly and with minimal losses. For that purpose brilliant minds like Tukhachevsky emphasized the strategy from which Deep Battle and Deep Operation doctrines were created - use of mobile forces to penetrate defences, in that time it was usually cavalry, armoured cars and armoured trains where applicable, and to continue exploitation far into enemy rear, never allow him to form a new defensive line or regroup. You see that its practically the same doctrine applied by the Wehrmacht and the Red Army in WW2, only with WW1 weapons. There were similar lines of thought in all major armies of the world but only in the Soviet Union that doctrine received official support and was codified as army doctrine in the manual of 1936. I assume you know how much difficulties Manstein and Guderian had when they tried to push their plan for attack on France, not just by Hitler but also by other senior commanders like Halder.
In the thirties Soviet adopted tank as the main weapon for such a doctrine. The first doubts begin to appear after the Spanish Civil War. Tanks of the time still weren't advanced enough, Soviets had problems of coordinating with Spanish infantry, that infantry was of poorer quality than the Soviet etc... All in all, tanks didn't perform as well as they should, but instead of identifying the correct reasons, committee set up to investigate it came to the wrong conclusion. That conclusion was also politically motivated as it was in the same time frame when Purges began. Tukhachevsky and his "faction" was purged, which incidentally involved majority of more open minded officers, leaving half-idiots like Voroshilov in charge of the army. One of the few Tukhachevsky disciples that survived was Zhukov, most importantly because he was relatively young and in the Far East at the moment. In general Far Eastern armies and their commanders weren't touched because they were too far to have any influence on politics and because of growing threat of Japan. Zhukov also had more prestige after Khalkin Gol. Although Khalkin Gol in 1939 showed what Deep Operations doctrine when performed by skilled troops and competent commander was capable of, it wasn't enough to vindicate it. Red Army deteriorated in a much worse fighting force than it was in the mid 1930's. It lost half of almost all officers in the army. What vindicated Deep Operations ironically was Wehrmacht's success in France and the Low Countries and partially it's relatively good application in the later stages of Winter War under Timoshenko.
So, in 1940, Red Army started another very slow, reorganization to make itself more similar to the mid 1930's and Wehrmacht. Soviets expected the reorganization to be finished in 1942. Also, under growing threat of the Germany, Soviets for the first time in a long time started looking at defense. In January 1940 two war games were held, practicing both defense and counter-attack. In the first Zhukov led the attack (enemy) while Belov led the defensive (Soviet) forces. Defensive forces were thoroughly beaten, prompting the Red Army to rethink its defenses. So another reorganization was started.
Lack of skilled officers of course slowed down those reforms. How serious was this lack after the purges show the example of then major later general Biriuzov, who had to assume command of his division because 4 higher officers were either killed or imprisoned. That position required at least three ranks and 10 years more experience than he had at the time.
Furthermore, after the purges, hierarchy in the Red Army was so complicated and huge that commanders often didn't know what to do and who to listen to. That was a part of Stalin's paranoid attempt to control totally every part of the Red Army. Orders were given in sealed envelopes that weren't to be opened unless several officers and political komisars were present, supply depots were sealed of until given specific orders from Moscow etc... In the chaos of the initial German attack many officers were dead so young and inexperienced officers were fearful of opening up the envelopes because they knew what can happen to them. Sure there were some commanders who showed initiative, like Rokossovsky, who refused to wait for the missing officers and practically stormed the depot and disarmed the guards who refused to allow him access, but that was the exception rather then the norm. Also Soviet troops were deployed without any logic. Forward positions were thinly manned not to provoke the Germans. The communications were in breakdown, partly because of German skillful disruption of communication line and partly of the impossible communication and command structure added to the confusion. Troops were given contradicting orders by various officers and Stavka couldn't get accurate information and assessments from forward position. Commanders were simply fearful of reporting just how terrible the situation was. That resulted in Stavka giving orders that were impossible to execute, for example an order to advance given to several division which were to be supported by several more. Problems those divisions that were supposed to provide support didn't exist anymore except on paper. That spelled certain doom for other division. In general, because of not knowing the situation Stavka and Stalin insisted on performing the counter-attack as planned. Of course it was impossible under the circumstances. Many forward supply depots were already taken by the Wehrmacht, there weren't enough supplies, ammo, shells, tanks, artillery and men to do it. Unfortunately, most commanders, knowing what may happen if they don't execute the orders simply started attacking allowing Germans to inflict massive casualties and to capture unimaginable amounts of enemy troops, equipment and supplies. There were some, again most famous example being Rokossovsky who retreated and saved what he could save but it was again the exception. Stavka, after seeing the disaster started to send representatives to bring back correct reports from the fronts. Indeed, Zhukov and Vasilevsky spent a good portion of the '41 just going back and forth from front to Stavka, for that only purpose.
Red Army lost huge amounts of equipment and weapons and their best troops. It lost majority of T-34 tanks, a huge number of airplanes, supplies, artillery, ammunition. That prompted another reorganization as Nazi advance continued. Tanks were no longer plentiful enough to form separate mechanized or tank corps, especially anything remotely similar to German Panzer Armies. They were relegated again to supporting roles. There was severe shortage of skilled commanders, mostly due to the Purge but German attack didn't help either, shortage of trained soldiers, shortage of tanks, airplanes and artillery. Under those circumstances, Deep Operations were off the table, as Zhukov, Vasilevsky and other Stavka members correctly assessed. On purpose, they brought back the Red Army to a far more primitive state than it was, using simply weight of numbers to wear enemy down and slow him down until the relocated industry starts producing again. Few skilled troops were put under competent commanders and organized into shock troops and given what was left of good equipment. The occasional glimpses of well executed delaying actions and counter-attacks in 1941 were performed by these troops. Zhukov and other leaders of the Red Army knew they had to wait until relocated factories produce enough weapons and equipment and until new soldiers acquire experoence and commanders mature enough to perform Deep Operations properly. That was the basic principle behind practically any decision by the leadership of Red Army until mid 1942. The occasional counter-attacks and counter-offensives were performed to slow down the Wehrmacht, rather than to regain huge swaths of territory, although Stalin often intervened in that regard.
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