The leader is a raving loony, but his scientists aren't. That's usually a bad combination. Look at Fred Phelps, he does what he does more to simply be paid attention to than out of any real conviction, he's figured out that being a complete bastard is a good way of being noticed. The leader of S.Korea is deliberately baiting Japan, in my opinion. When he first announced his nuclear attentions, he was complaining about being watched by the world, now he is complaining that no-one is looking at him, hence this recent 'tantrum'.
It's a pity, North Korea has a lot of potential, but the legacy left by this guy is going to take years to repair in that country, nukes or not.