With a little more work, this has the potential to be something special. I mean official content kind of special. As it stands now I'm still rating it 5 stars just because it's so ambitious and nearly pulls it off. Btw, the hot air balloons look great, but unless you plan on animating them, I'd lose the choppers. Outside of that, it's pretty epic.
I reccommend playing with 5-6 other ai/players max.