Nice game, but I would appreciate some score/goal, because now it seems useless to build engines. Also camera rotation feels weird, as the controls leave the same. I would recommend adding some UI as well (and not many buttons which do something).

Game looks and sounds great, its bit hard to understand what you can and should do, also there doesn't seem to be an end game, whats the benefit of shrinking? What is the energy used for?  should we supply an increasing demand of a city or something? A level system or waves of enemies and highscores would be nice