While Soviet tanks have thinner armor than other nations, they make up for it by having highly sloped armor which increases effective thickness and a higher chance to ricochet shells. Their guns also pack the most punch in the game and along with their good speed, maneuverability, and armor characteristics, make them kings of close combat. Their downside is that they have poor accuracy and aim time, and in some cases a low rate of fire.
Soviet light tanks are typically the fastest in the game and, like most Soviet tanks, have a small frontal profile and sloped armor.
Soviet medium tanks are also fast and maneuverable, and equipped with accurate guns unlike the other lines in Russian tree (and gets even better in high tier). All are jacks of all trades and very versatile. Unfortunately, most suffer from poor gun depression, limiting their ability to go hull down and makes use of their strong frontal turret.
Soviet heavy tanks have the best values for everything except accuracy, aim time, and view range; their frontal armor thickness and slope makes them quite difficult to penetrate from the front. There are two lines: the KV line which offers thicker armour and standoff potential at the cost of mobility and the IS line which has armour more reliant on angles, but better agility and alpha damage for brawling.
Soviet tank destroyers have bad armor but they have best camouflage values in game. They offer increased speed, agility, and brute firepower. There are two lines: the Object 268 line which favours alpha damage and the Object 263 line which favours mobility and Damage per Minute.
Soviet self propelled guns are generally quite accurate but don't do much damage. However, they also generally fire their shells in a very high arc, making their flight time long, but able to hit tanks hiding behind rocks and small buildings. They also tend to have higher firing rates than their foreign counterparts.