Pretty much just save your money and buy turrets. For the different ages, whichever most expensive unit is (dino rider, knight, etc.)put a ranged unit behind it. If ur saving money than put the least expensive unit , and then a ranged person behind it, and keep doing that. MAKE SURE YOU BUY TURRETS. one of the most important things to do. You probably have no chance at winning without turrets. On hte last age put a bunch of the least expensive unit out...like A LOT OF THEM and then get the supersoldier, by doing this the (least expensive unit) will gain ground for you supersoldier so once they die he can go in for the kill.
yeah, turrets do all the work on normal. They're pretty important. Also, throughout the game, I like to keep the battlefield like this: -That way turrets give you an edge- B)=base O= your guys E=enemy
iv'e never played on impossible mode but normal and hard are easy. just when you can evolve to the next age-DONT.that way it will be harder but u get double money. then wen the PC is 2 ages ahead of you THEN evolve 1 age. So always stay behind the computer one age. BUT when you get to the army age stay on the same age as the comp and also the alien age. I hope you were able to understand that gobbledeygook but if you were then try it.
On last age buy 4 ion turrets and nothing else, save up for 2 super soldiers and let the turrets do the killing for the stuff that comes near your fort.
use the weakist guys, because you can buy more of them and the more you have the more they attack. NEVER BUY SUPER SOLDIARES THEY ARE A WASTE OF MONEY!