I can think of a list of things which either excelled at the time or were feats not matched in the whole war.
Some, like the T-34 and Yak-1, excelled in the early period of the war with clear advantages in technology and numbers (a superior weapon is no good if there's not enough of them), but their advantage faded as technology advanced, yet they remained viable front-line systems through the whole war. Others, such as production miracles or use of artillery, were feats not to be matched in the whole war.
Keep in mind that an excellent weapon system is not just the one with the best attributes, but also produced in significant numbers to make an impact on the war ("quantity has a quality all its own"). It has to fit the battlefield conditions and be usable within a soldier's (often inadequate) training. It has to be easy to transport and maintain, or expected to be destroyed so quickly that it doesn't matter.
All of these weapons exemplify a style of equipment to meet the needs of the Soviet army. They're as effective as German equipment. They can be effectively used by poorly trained soldiers. They can be cheaply and simply made by a severely disrupted industry. They don't need to last long, because they'll probably be sacrificed, and there's more on the way.
I'll go into each of them in some detail.
The T-34 excelled, particularly in 1941.
- Appeared in 1940, very early in the war.
- Excellent use of sloped armor.
- 76mm high velocity gun superior to most tanks in 1941.
- Good cross country performance.
- Cheap to produce.
- Easy to produce.
- Continuously upgraded through the war.
- The basis for a number of very successful variants.
- Awful ergonomics.
- The 2-man turret overloaded the commander who also had to load or fire the gun.
- The armor became inadequate in later years.
- Unreliable transmission.
- Bad optics.
In 1941, when the Germans were slicing through most Soviet tank formations of BTs and T-26s, the T-34 was a shock. With a better gun and armor than the German dedicated anti-tank tank, the Panzer III, a well positioned T-34 could hold up many times their number.
Half a dozen anti-tank guns fire shells at him [a T-34], which sound like a drumroll. But he drives staunchly through our line like an impregnable prehistoric monster... It is remarkable that lieutenant Steup's tank made hits on a T-34, once at about 20 meters and four times at 50 meters, with Panzergranate 40 (caliber 5 cm),[nb 1] without any noticeable effect.
The Germans retooled their entire tank production to deal with the shock of Soviet medium (T-34) and heavy (KV) armor. The upgunned Panzer IV, the Tiger, and the Panther were all rushed to deal with the surprisingly well armored Soviet tanks.
The Soviets built heavy tanks like nobody else, and the IS-2 was the ultimate example. It not only was a more balanced design than any other heavy tank, it was built early enough and in large enough numbers to have an impact on the war.
The British Churchill was slow and woefully undergunned. The German Tiger I was finicky and expensive, while the Tiger II was a bridge crushing 70-ton beast; neither were built in sufficient numbers to affect the war. The Americans eschewed heavy tanks entirely until the very end of the war.
The IS family evolved out of the powerful but unbalanced KV-1. The KV-1 had extraordinarily heavy armor for 1941, but it was undergunned, underpowered, unreliable. Attempts to improve upon the KV-1 lead to the IS-2.
By 1943 the T-34 was already being armed with a very respectable 85mm gun, so the IS-2 was given a monstrous 122mm gun. This gave the IS-2 very good anti-tank penetration, but also a very large high-explosive shell for use against German fortifications, (a consideration that is often lost in appreciating tank design is that tanks fight infantry far more than they fight tanks). The enormous shell could bull its way through the front armor of a Panther at 2500m.
While the IS-2 was a "heavy" tank, it weighed the same as a Panther medium tank, but with heavier armor and a much larger gun while retaining similar range and decent mobility. This was a far more balanced design than either the Churchill or Tigers and sets it apart.
The other area where the IS-2 excelled is production. Despite being introduced fairly late in the war 4000 were produced compared with 1400 Tiger Is and only 500 Tiger IIs. While nothing compared to the volume of T-34s, it allowed them to have a significant impact on the Soviet offensive as a breakthrough tank.
The IS-2 lead to the IS-3, a tank which gave Allied (and later NATO) planners serious pause. Together, the best elements of the IS-3 and the T-34 would be combined to produce one of the most influential tanks in the world: the T-54 main battle tank.
The Soviets focused on producing and improving three hulls for their armored vehicles, the light T-70, the medium T-34 and the heavy KV/IS line. Their tanks and tank destroyers were all iterative improvements of these three hulls allowing a continuity of production and design. This avoided the long teething problems and retooling of brand new designs so high production could be preserved.
In contrast in 1944 the Germans were producing seven hulls and still introducing new ones (the Tiger II) when they should have been focusing on producing known designs. The British also had a dizzying array of production and experimental hulls. The Americans came closest to the Soviet achievement by focusing on the M3/4 medium and M3/5 light, but they also built the specialist M22, M24 and M18 in large numbers and never managed a heavy tank in numbers like the Soviets.
The legacy of this focus on just a few tank models lead directly to the idea of the main battle tank.
While there are better aircraft in WWII, the Yak-1 and Il-2 stand out for what you'll start to recognize as a Soviet pattern: early entry in the war, matching or beating their contemporaries, continuously improved, and produced in enormous numbers.
The Yak-1 (and its many variants) was equivalent to a BF-109 or Spitfire and it was the aircraft that held off the Germans through the whole war. It is the most produced fighter in history with 37,000 produced.
The Il-2 "flying tank" was a revolutionary dedicated ground attack aircraft. Heavily armed and armored, it could (and was) flown by crews with little training. 42,000 Il-2 (and variants) where made making it the most produced military aircraft design in history.
Due to its inaccuracy its actual effectiveness is debated, but its distinctive design, huge numbers, and legacy on ground attack aircraft design is solid directly inspiring one of the best ground attack aircraft, the A-10.
The PPSh-41 and PPS are not particularly remarkable submachine guns, not much better or worse than contemporaries. It isn't the gun itself which excelled, but how many were made: 7 million during the war. This is more than twice production of the MP 40s, M3 grease gun's, and M1 Thompson combined. The only equivalent gun is the Sten gun.
It was becoming increasingly apparent that ranges of 10 to 300 meters were the norm in battle and short range firepower was what mattered. In a war still being fought with bolt action rifles designed for aimed fire at ludicrously optimistic ranges (2000+ meters), the Soviets were arming whole companies with cheap submachine guns to close with and chop up the enemy.
The Eastern Front of WWII was fought on a scale that the Western Front wouldn't see for two more years if at all. To give one example for comparison Operation Uranus, the Soviet counter attack at Stalingrad, was fought with 1 million Soviet troops, 1000 tanks, 1500 aircraft, and 13,000 artillery pieces. And this was November 1942 on a single front. At about the same time the British were fighting the Second Battle of El Alamein with 100,000 men, 500 tanks, 800 aircraft, and just 500 artillery pieces. The scale of fighting on the Eastern Front would not be seen in the West until well after the Battle of Normandy.
On the theme of doing it before everyone else, the Soviets concentrated artillery in ways that only the Americans would begin to match in late 1944. Again, Operation Uranus concentrated an accurate barrage of 3,500 artillery pieces on the Third Romanian Army. Massive, crushing artillery barrages would continue to be a feature of Soviet offensives all the way to Berlin.
One of the most overlooked Soviet achievements of WWII was evacuating its industries away from the advancing Germans and to the Caucuses or behind the Ural Mountains out of reach of German bombers (and also highlights the German strategic error in not investing in a heavy bomber).
This is a feat unparalleled in world history and caused unimaginable hardship as entire populations were moved thousands of miles and forced to create cities and factories in the middle of nowhere. Despite having a large portion of their country overrun, the Soviets maintained industrial output through the war.