The Kamikazis make it interesting. You definitely can deal with them with a little effort. The obvious most useful weapon is mines. If you know where the kamikazis are going to enter, you don't put valuable resources nearby and you figure out where to put the mines you'll use to blow them up. I've also found that fully matured cannons can shoot them at a distance and destroy them before they have a chance to do any damage. The castle is the most difficult level I found for kamikazes, and only for the ones that enter at the top right of the play area. It is difficult to avoid losing good resources when they are blown up, but I've beat the Castle level, with its kamikazis, on the insane level of difficulty. The only one I still have not conquered is level 19 at insane difficulty, and I'll admit that level 20, the new one, is giving me some fits.