How possible was it for the Eastern Front of WWII to become a Vietnam-style War for Nazi Germany? Where they make initial gains at first but then the Soviet Union goes full-on guerrilla warfare and the German forces are unable to really deliver a knockout blow so to speak? Would the vastness of the Russian steppes be an advantage for the Red Army or would the openness of the terrain also be a disadvantage (unlike where the NVA and Viet Cong could hide in the Southeast Asian jungles)?