I beat it on very hard mode... without realizing I could scroll so I had 8 properties unused, after figuring it out, pollution was negative in both cities, and much more money coming in
max out natural gas, you can place them inside your defensive hill on the last level, trucks run long pollute less on it, and the oil can run FLAME TURRETS
gravity Gun is useful throughout the game, but once past 40 you want at least a chain gun to back you up and pepper bosses so they keep their shield up/die
giants were nearly unstoppable until I started hitting them with speartons rather than trying to dodge with swordwrath, max upgraded speartons can drag down a giant, especially if you take one over and hit it from the back. final boss was HUGE