German tactics were often hampered in the East by Hitler's refusal to lose any ground. This forbade strategic withdrawals. Incidentally, Stalin's orders were very much the same in this way. It seems that both failed to realize just how vast the distances were in Russia and how important mobility was to armored forces.
As for the German military itself, I would say that it was simply not up to the tasks it was presented with. Defeating France was easy because the objectives were all relatively close to Germany, so the initial French blunders could be exploited, leaving the allies no time in which to turn things around. Russia's initial deployment was certainly as incompetent as France's, however Russia was given time to mobilize and put up serious resistance. When a tactical victory was possible, the Germans capitalized on it. When, however, Hitler's orders and the great distances involved prevented one, the Germans simply were unable to win the resulting slugfest because they had too few resources, poor supply lines, and not enough troops to hold such a long front. Plus they really screwed up at Kirsk by waiting for their newest tanks. I would say it was probably more decisive than Stalingrad, considering their heavy dependancy on mechanized forces and losses in that area.