The Kraken is really useful when maxed. But then it's a beast. Sometimes it can be useful at 1 BCX, for example in 'lost all abilities' kind of game with no mana cap (99).
Update: Combine the Kraken with 2 tank heal monsters (which Water has), and as a bonus Byzantine Kitty, and you have a very high chance of winning the game. Not if the opponent has affliction or has high attack power magic monsters, in which case you will probably lose.
Maaan...You should write a strategy guide ;)