took me some tries to figure out challenge n. 5... but the key is not try to build ANYTHING in the first day: get an oil rig, a couple of guns to defend your base, and disable the coal AND the farm. then, if you survive the first night, smog will be really low. final score over 5K.
great game, great content, and GREAT ending song!
needs to be more balanced, tough. some paths (weapons, energy sources, etc) are MUCH better than others.