Exit polls suggest the Liberal Democratic Party of Japan has been ousted after being in power almost continuously for the last 50 years. See this CNN.Com/Asia article for a quick overview.
Countries where one party always wins the election are less-than-fully democratic. As Lord Acton said in 1887, "power corrupts, absolute power corrupts absolutely." Eventually a long-governing party generates its own downfall.
Mexico's many years of rule by the PRI was another example of this phenomenon. In both Mexico and Japan there were opposition parties which for decades amounted to little. However, now in both countries opposition parties have won power at the national level.
This election is an important milestone for representative government in Japan. Regardless of the DPJ's policies, its election in Japan is a positive step for representative government there.
On the other hand, there are press reports of the new leader's wife believing in UFO abductions.
