For me, the September Campaign would've been over much, much quicker if the Soviets weren't so overzealous about using strategies. I had to conquer each production facility several times, and then some. Was fun, though. :D
A ship with nothing but Lvl5 rocket launchers was bested by a ship with nothing but Lvl1 lasers. I don't even want to imagine how powerful a grid full of Lvl5 lasers would be like. :P
Lvl4 is quite easy - You just use your tanks to get the barriers, and use the rocket and mortar trucks to get the spider tanks together. When your tanks reach the warfactory, use them to get the spider tanks while your mortar and rocket trucks come over to get the scorpion tank. Finite! :)