I haven't played world map since it was released (played a couple of games right after release) but a few things I remember about it:
1) The Chinese are too weak. Japan will basically crush China 99 out of 100 games if they want to, it's not very difficult. Something needs to be done to (in my opinion) deter Japan from trying to conquer China - maybe super partisan reaction, or an event that reduces JP income by 100 every turn that they hold key Chinese cities - something really painful for Japan that causes them to want to avoid entering the interior of China. I'm no expert on the war in China but historically the Japanese were unable or unwilling to advance deep into China. On the other hand we don't want super-China so something has to be done to make it hard for the Chinese to hurt the Japanese much or in particular advance out of China. Maybe Chinese units can all have 1 attack value but high defense values? China should be a distraction for Japan but not a situation that is "winnable" the way it is in this game.
2) The map just seems too small. I wish that the map had double the number of hexes. It feels very strange to be operating with so few hexes on the Russian front, in France, etc.
3) The pacific war felt weird. I didn't see a lot of reason for Japan to advance into the Pacific at all. They seem better off stopping at Philippines and Indonesia and focusing on India and China and Siberia.
(1) I think cranking up the number of partisan hexes (both kinds: units and anti-supply events) would be the most reasonable solution.
(2) After slaving away on an enlarged version of the Euro map for 4 months now, I am now well aware of the massive work that would be involved. But yes I'd love to see a full 512 x 256 hex map (annnd someone said that there was a workaround allowing an even bigger one, using the map-to-hexes utility). I've actually been trying to talk myself into doing exactly that, since I am an IJN fanboi of sorts.
In any event the Pacific-only map in the Scenarios subforum is ~95% done in terms of terrain, and has a more acceptable scale (since it is based off of Grigsby's WitP map).
(3) Despite my proclivities alluded to above, few AARs ever seem to have any massive Pacific naval battles-and the AI can easily be divided and conquered (in one game I sunk like 40 USN units while only losing 3 of my own). I decided to stick with the Euro theatre because the AI there is more "mature."