Morning Sun starts in 1937 when Japan attacked Beijing (Beiping) in China, so that means we have here a lot of pre WW2 units, for exemple the Chinese army have some FT17 tanks (French WW1 tanks !!!), a lot of pre WW2 old planes.
The Chinese have a bigger number but their army is crappy and not very well equiped, they use mostly some imported armamement like Italians canons, German Panzer I, Soviet T-26 1933 Version tanks, English Hawke III planes or Soviet Polikarpov planes, on the other hand the Japanese have less soldiers but their equipement is more modern and better, they have a good infantry (they can do Banzai charges), they have some pre WW2 tanks like the Type 89 etc.
So we have a lot of old stuff and equipement and that's very funny to play because it's different from what we know, for most of us we only know the stuff from WW2 so here we can learn and see something new.
The missions are nice, we have 2 missions with some landings on the coast of China but it's mostly some heavy infantry fights on the mainland of China and that's pretty much cool.
And you can keep your army and import it to Rising Sun. So buy Morning Sun and Rising Sun and play it one after another.