Kv2 is an ISU with a turret minus the range + tons of deflection damage. I can't say that Siege mod is very useful, unless you 100% sure that you won't be punished and the guy is AFK with his units. Also works if you are able park it behind some shot blocker and camp the VP, like on Eindhoven Country + it has tons of scatter. The tank is superb, but I'm not a fan of the ability. I would not pick it in team games tho, even in 2v2. If you intend on using the ranged ability, just pick the ISU. Much more convenient.
Imo KV2 is the closest Allies have to KT.
The kv-2 siege mode lets you setup a long range artillery piece that can hit whatever whenever
While its obviously not useful in offensive situations, it is great to let you dig in and destroy squads that are approaching. Sprinkle a lot of zis guns around, or SU-85s if you got the fuel, infantry in cover, some mines in your flanks (or spots where you can be rushed from). You make a defense that's really difficult to break without diving the kv-2
Its a beautiful tank and makes the is-2 obsolete, the kv-2 works in team mode well enough to be viable - siege mode lets you be useful against heavy TDs as you don't get in their range to do your damage