Let's see. Some people in this thread have mentioned that Korea might turn communist. But honestly, I doubt it.
Here's my reasoning. There's still a Provisional Government of Korea in China. If there is a post-war attempt to form a united and neutral Korea, the Provisional Government would most likely take the lead and become the new leaders of Korea. The only reasons why Kim Il Sung became the leader of the DPRK was because he was seen as a "communist revolutionary." The only reason why Rhee became the president of the RoK was because he was anti-communist. So.
I mean, I could definitely see Korea becoming friendly with the Soviets (various reasons, USSR is right next to Korea and Korea's arch enemy Japan has aligned with America), but I don't see an upright communist revolution to take the entire country. Under the rule of Japan, the Communists were beaten up pretty harshly and most of the left wingers fled to the Soviet Union (including our dear leader Kim Il Sung). I think the new government would be democratic in a sense, similar to Austria of our timeline.
Without a internal war, Korea will have the infrastructure and industry from the Japanese occupation And since Korea is neutral, it'll possibly have a smaller army than OTL. So I could see that Korea will have some benefits of being a neutral nation and economically thriving (north has plenty of mines and resources that can be exploited while the south has the industries and the population). Not a powerhouse, but still well off (always in China's shadow though).
I'll take a careful guess and say that this world's Korea will be economically bigger than OTL's South Korea (I would shoot around $2 Trillion economy). Why? Because resources, neutrality, a smaller military (no north and south rivalry), and an intact industry post WW2 will allow Korea to have a better start. Bigger population to, due to no major famine of the 90's in the north or prison camps or communist purges. So a population of around 75 million, with a $2 trillion economy. So around $27,000 GDP per capita. Still very well off. As for alignment of modern times, I would think that Korea would become the "Switzerland" of Asia. I mean, Korea does have it's fair share of time of being a Hermit Kingdom and if given a chance to remain independent and neutral, I would believe they would stay independent and neutral. Besides, what would benefit them if they allied with either side?
As for government, I think Korea will maintain a democracy. I mean, Koreans revolted a lot of times to maintain their democracy and if we're going with something similar to Austria, than Korea will definitely stay a democracy. And without economic problems and political problems from the beginning, I think Korea won't have the military coups and dissent it had in OTL.
A few other things to note: Korea will most likely not be afraid of the left as much as OTL. They'll most likely take several directions closer to the left, similar to OTL Europe. That would mean no bans on the Communist Party or communist literature and the such.