The IS-4 is very versatile, with decent speed and weapon power, and sloped armor. It's side armor and rear armor is stronger than it's frontal armor. It's guns are somewhat innacurate, but damage and penetration is strong.
It's strengths include it's ability for a heavy tank, sloped armor, and high damage and penetration.
It's weaknesses include low turret traverse rate, frontal weakspot, and low accuracy cannons.