May be a bit of nit-picking, but I do not agree with the characterization:
It was a development of the IS-2 ….
Like it's predecessor, the IS-2 …
At least in terms of developmental pathways, the IS-3 was not a follow-on to the IS-2, nor developed from the IS-2.
The original IS-85 (later re-named IS-1) was developed from the KV-13, using a prototype version of that tank identified as Obj. 237. This was further refined in Obj. 240 into the IS-2 by redesigning the turret and mounting (eventually) the 122mm D-25 gun. Both the original work and the redesign was done by Kotin's team at the Kirov design works at UZTM.
The IS-3 was an alternative to the IS-2, a separate developmental path, by a separate developmental team, taking the starting point of the KV-13 components and the D-25 gun, but going a different direction with them. This work was done at Chelyabinsk design bureau at the ChTZ factory, under the designation of Obj. 703.
If one wants to see the further development of the IS-2, I think it is Obj. 701 that one should look at, which came into service as the IS-4. This project, carried out at LKZ, enlarged and up-armored the IS-2, retaining all of the comparative advantages of that design vs. the IS-3 path.
The IS-3 was very influential on future Soviet/Russian tank designs, but in itself was not a very successful tank. It never replaced the IS-2 in service, and in general the IS-2 was considered to be operationally superior to the IS-3.
The IS-4 was probably a better tank than the IS-3, except that it was notably larger and heavier, and those were key concerns of the Soviet military. The Soviets put a great deal of focus on logistics, and could see that the IS-4 would bring many challenges in operational mobility, particularly to a force with an offensive orientation, being a tank that exceeded loading limits on railways, bridges, shipping, etc. So it was only produced in limited numbers and mostly left to provide defensive firepower on the far-eastern border with China.
Or so I have read. Never seen an IS-4 in person, and certainly was not present during the development of any of the Soviet heavies.
-Mark
(aka: Mk 1)