the ISU wasent even very heavily armored. a 90mm sloped plate would by NO means deflect 88's. i am consufsed why the game deisgners gave it more armor then the KT.
check this:
http://en.wikipedia.org/wiki/ISU-152The ISU-152 was developed further during 1944. A new hull front was added and the gun shielding was increased from 60 mm to 100 mm.
The vehicle's excellent armour protection finally provided the 152mm platform with good protection from most German AT guns, allowing it to advance into the face of direct AT fire, while the huge low-velocity HE rounds were excellent at blasting open even the most heavily fortified and reinforced enemy strongpoints.
The ISU-152 could also operate as an effective ersatz heavy tank destroyer. Though it was not designed for the role, the vehicle inherited the nickname Zveroboy ("animal killer") from its predecessor the SU-152 for its rare ability to reliably kill the heaviest German armored vehicles, the Tiger, Panther, and Elefant.
The weight of the 152mm shells made for an extremely low fire rate, only one or two shots per minute, and they were not as accurate at long range as high-velocity antitank guns, but the massive 98 lb HE charge was capable of blowing the turret completely off a Tiger from sheer blast force alone. No tank crew could expect to survive a direct impact from a 152mm round, though the chassis itself was sometimes salvageable. For anti-tank operations following the Battle of Kursk, the even-larger 102 lb. BR-540 solid-core armour-piercing round and charge was developed, with an eye towards giving the howitzer a more traditional AT capability.