In Poland, the Russian advance has been ground to a halt. German forces, numbering over 1.5 million, have managed to stalemate a force more than 2 times larger.
The disparity in equipment quality and training is to blame for the Soviet's failure to push further into Poland. Green, novice Soviet conscripts, most of whom have never handled a rifle before, are facing off against veteran German soldiers.
While the Russians have the AK-43 assault rifle, the Germans Stg43 rifle is more than a match for the Soviet rifle. Both of them are roughly equal in their capabilities, however, the Stg43 rifle has been in service longer than the AK-43 and the Wehrmacht is more familiar with it's strengths and weaknesses than the conscript Soviet army.
The German Kar98k rifle is arguably better than the Mosin Nagant 91/30 rifle, as the Kar98k is shorter, easier to handle, does not used rimmed ammunition, and is generally of better quality than the Soviet bolt action rifle.
The greatest difference, however, is between the German "Panther" Panzer V, and the Soviet T-34. The Panzer V outranges the Soviet T-34 by more than half, and even at close ranges the T-34 has difficulty piercing the frontal armor of the Panzer V. To compound this the T-34 lacks a decent radio, decent suspension, and is slower and less maneuverable than the Panzer V. In the wide, flat expanses of Poland, the Panther's superior optics mean that 75% of the time the Panther will achieve a one-hit kill on a T-34 before the Soviet tank is able to spot the Panther.
Even though the T-34s outnumber the Panzer Vs more than 4 to 1, the appearance of the Panzerfaust- a disposable anti-tank weapon carried by one man- mitigates this advantage in numbers. Entire companies are being armed with this weapon, causing considerable damage to advancing T-34 tanks that roll over trenches and into obstacles such as barbed wire and Czech hedgehogs.
The Germans maintain complete air superiority over the Soviets. The Me-262, the first practical jet fighter to fight in the second great war, ensures that no Soviet plane gets off the ground. The Me-262 simply outguns and outruns any plane the Soviets can currently produce. The Luftwaffe have total control over the skies- there is simply nothing more to say here.
The casualty rate of the Soviet Army is heavily disproportionate to that of the Wehrmacht- nearly 650,000 Red Army soldiers out of 4 million have been killed or wounded, compared to only 115,000 Wehrmacht and SS soldiers killed or wounded. 297 German tanks have been destroyed or disabled beyond the point of repair, while over 1,180 Soviet tanks have been destroyed or disabled.