unfortunate bug, but a game with serious potential
I like the mobility factor in this "tower" defense game. it's definitely innovative, and i think with further refinement (ahem, sequel?) it could set this game (series?) apart from other tower defensers.
as it stands, i noticed the "white screen" bug when i "lost focus" on the window, as it were, and went to itunes and then came back to it. you can still see the units, the map is still usable (ie. i can airlift to the points that should be airliftable, etc) but i can't really see what's going on, and can't see the menu either. after the level finished i tried clicking where the "start wave" button should have been, but to no avail. Given that problem, your score is lowered. as it stands, i'll give it a go without switching windows and see how it goes. i think this is a game worth revisiting, and i will be doing so later on in hopes of seeing updates and all.
oh, i'm sure some people will be crying for music or whatever, but if you do add it, also add an option to turn off the music (but leave the sound on), because that's an instant 5 in my book. ^_^
Good job, over all.