The IS-2 M1944 (Iosef Stalin, also known as the Josef Stalin or Stalin tank) is the heaviest tank available to the Soviets in Spring 1944.
The IS-2 was developed to replace the KV series in Soviet service and counter the increasing numbers of Tiger I and Panther tanks being fielded by the Germans. Although heavily armored, the KV-1 was no better armed than the medium T-34, less mobile, and considerably more expensive. With a more efficient armor layout and a monstrous 122mm main gun, the IS-2 was more mobile and packed a much heavier punch. Despite its formidable armor and weaponry, it was actually about the same weight as the "medium" PzKpfw. V Panther. First fielded in April 1944, over 3,000 were produced. Typically deployed in heavy armor regiments of 21 IS-2s, they were used to smash through enemy defenses and allow lighter T-34s to penetrate enemy lines.
Despite the fearsome caliber of its main gun, the IS-2 is not as efficient at antiarmor duties as the German Tiger series. The medium-velocity D25-T 122mm gun has about the same penetration capabilities as the high-velocity 75mm and 88mm guns fitted to the Panther and Tiger I, although it has a longer range than the Panther's KwK 42. Additionally, the large two-piece shell and propellant charge severely limits both the firing rate and ammunition capacity of the IS-2. Nevertheless, the IS-2 is the only Allied tank in the game with the range to engage Tigers in a long-distance gun duel, and its heavier armor will allow it to defeat a Tiger I in single combat (although the Tiger can outrun the IS-2). It is tougher than the Panther but can be outmaneuvered by it. In general, the IS-2 is a formidable opponent, only outclassed by the Tiger II, and its long range and powerful high-explosive shells make it extremely devastating to infantry and fortifications.
When using the IS-2, you will notice that it can never really decide if it's a heavy tank or a mobile artillery piece, so it kinda does both jobs. The turret turns very slowly, but the range is something you'll want this tank for for sure. In most cases, medium tanks stop exsiting after just one well placed shot. Anything heavier will require some shelling, which is where you'll see the artillery aspect: reload times. Those usually come with the great range, but in the case of the IS-2, it also comes from nearly perfect accuracy - something you'll be looking for after using the ISU-152. What you should be worried about are things that your IS-2 can't blow up reliably, because usually those are the same things that can deal any form of damage to said IS-2. These are situations when you should opt for the cheaper and more devastating ISU-152.