Death has seldom come to a more deserving person. In addition to putting North Korea's economy firmly into the crapper, Kim and his father (Kim Il-Sung, founder of the nation) oversaw a network of concentration camps, kidnapped Japanese and South Korean citizens, and regularly engaged in state-sponsored terrorism (bombing civilian airliners, shelling South Korean towns, etc.). Outside of North Korea, few people responded with anything short of "hallelujah" to Kim's death.
The trouble in North Korea may have only just begun. Kim Jong-il's son, Jong-eun, is the heir apparent, but he's young and untested. Moreover, as I wrote last year, a dynastic power transfer in North Korea increases the risk that the ruling coalition breaks down, inciting internal - and perhaps international - strife.
And, in the event that Kim's death has made you optimistic about Korean reunification happening sooner rather than later, I will refer you to this piece from last year. Be careful what you wish for.