the is2 alone isnt what make it great. it is great because:
1) it can be self repaired / accompanied with guards and their abilities
2) it can be defended against tiger if the tiger is winning by ramming a t34
3) it is usually supported by mines because soviets usually float loads of ammo in late game.
4) it can cap points on vet 1, very useful for recaping center in long games when most inf is dead on both sides
elefant is the real only problem this tank has i think.
Shock rifle frontline doesn't get guards nor self repair, armored assault doesn't get any elite infantry whatsoever.
Unless you mean team games, in which IS-2 is quite different.