Good riddance. I hope he died screaming in agony. It'd only be fair. No, wait, I hope he died, screaming and roiling in agony, regretting the millions he spent on primitive fission-based nuclear weapons, which he could have spent on better hospitals and competent doctors!
Without a doubt, he was one of the worst people who ever lived. Yes, the US isn't an angel. Yes, the West have done bad things - none of that excuse what that jerk did to his own people. I don't care who you are: the minute you force people to worship giant statues of yourself while they are starving, you deserve to die. And Kim Jong-il certainly deserved to die.
Sadly, I don't think it'll make a difference. His son is very much like him. The system of government is so rigid that it can't change without breaking entirely. In the best case scenario, Kim Jong-il's youngest son will swiftly consolidate power and things will continue on as they did before (I have no hope that he'll reform anything). In the worst case scenario, a number of generals and advisers will compete for power (like they did after Kim Jong-il's father died) and the situation will deteriorate, resulting in even worse famine for the North Korean people and potential military provocation from whoever leads the North as a demonstration of their "mettle". It's a long-standing tactic of the North: when things aren't going well or positions are threatened, they do stupid crap to the South to in bolster their "pride" or shore up their "credibility" as "Defenders of the revolution". Whoever the next leader is, he'll be sorely tempted to do something nasty to the south to show that "He Means Business".