I don't really have a high opinion of his work in post-war Japan, given that he was the reason that Hirohito stayed on and the reason why we never bothered to install a functional democracy there.
And in Korea, wasn't part of the reason why he was successful at Inchon due to the fact that it was a horrible place for an amphibious invasion, the NKs knew this and didn't bother guarding it, and he got extremely lucky with the tidal conditions?
That was why Inchon was so successful. It looked to be impossible, and was for most countries. Realistically the only countries on Earth that could have made it work were Canada, the UK and the U.S., with the U.S. being the one country with both the experience in planning and actual assault landings as well as the necessary lift and specially trained troops.
Inchon was a gamble, any assault landing is, but it was a good gamble.
Regarding the Occupation, he didn't really have much of an option. The NCA had chosen to leave the Emperor in place so he couldn't take Hirohito out and hang him, regardless of if he deserved it or not.
As far as democracy, I would say that Japan is a very solid example of civilian elected government. Yes it effectively a single political party with slightly different flavors, but so is the U.S. Japan's politcial system and justice system also reflect the "character" of the Japanese culture which is as it should be. The goal of the Occupation wasn't to turn Japan into the U.S., it was to make it a non-military dominated society. That goal was met.
As anyone who has ever read anything I have posted on the man knows I LOATHE MacArthur. Nevertheless, you have to give credit where it is due.