Basically, kind of a big deal - but provided that it's used correctly. Not how Pravda is shown to use it in the anime.
KV-2 had less than poor maneuvrabiliy and durability, but its armor could only be penetrated by FlaK 36 88 mm gun shooting into the rear armor plate, and its 152 mm howitzer was a menace. So the effective way to fight with it was what they did with StuG III in the Ooarai vs. Pravda episode: camouflage it properly and don't let it move. Extra points for digging square pit and hiding the tank inside it. If done correctly, a single or just a few machines could stop an entire tank regiment. - that's what I wanted to comment, but looking closely, the leading actor in the most if not all the stories about stopping an entire regiment was the KV-1 tank, not KV-2. There were just two hundreds of KV-2 ever produced, and most of them were not even lost in battle. They were instead mostly abandoned after breaking and deemed impossible to fix, or running out of fuel, as there were problems with supply (the same happened to early T34/76 which were practically invincible at the moment but mostly ended up abandoned).
So useless!!If you know how to deal with it, then even a KV-2 is no big deal!!Fleeing~!!!