Cabal Leader 1: The people have made so many changes since our time passed. We have much to do once they have been beaten again. Cabal Leader 2: In the old days, we could just take back the means of production. But they've got free Creation Engines on street corners now! Pumping out food and clothes for nothing! Solar energy collectors in orbit for Gods sake, beaming free energy back down! We need to bomb those fucking things out of the sky for a start. Cabal Leader 3: Obviously, we need to start from scratch. Major urban areas need to be taken back to the stone age. The infrastructure of their society needs to be wiped out. There can be no half-measures. Once that's done, we can go in, reintroduce the concept of money. Money for labor. Food for money. Without those basic relationships, there can be no control. Cabal Leader 4: And without control, we may as well just end all life on this planet and see if the cockroaches can get it right, a billion years from now.
Puma + Cloak + Flamer = You win. Always. The Puma doesn't show up on radar, the cloak prevents visual identification unless you literally run into a unit, and the flamer does damage-over-time that will destroy any small building. Simply drive up to the oil rigs, decloak for a quick burn, then recloak and run like hell. The enemy can no longer fight back except for defense. The flames will persist and consume the rig eventually, even if you don't do much initial damage. It works in almost every mission except the last one. It can be done before you get the flamer, too, but you're more likely to lose the Puma since there's no damage over time. Even when the enemy respawns them, you just need to fly a plane over as a spotter, then rinse and repeat. In the rare cases where the Puma's built-in firepower isn't enough (some missions stick a bunch of turrets around to discourage this), the fact that it's completely undetectable unless it moves too close to an enemy unit makes the Puma a perfect spotter for Antaeus' guns. This can make some of the more difficult missions (especially the second to last one, where the enemy are dug in hard and you're on a time limit) much, much easier.
In the final mission, the Vulture gets a massive damage bonus with the Warhammer, enough that five shots will demolish any construction facility. This is supposedly balanced by the fact that it has armor like paper mache and no slots for soulcatcher pilots (they'd botch it anyway). However, the Vulture becomes almost completely invulnerable if you simply point straight up and accelerate, sending your plane so high up that no AA can target it and almost no enemies can see it. Then just fly over the factories, bomb them out of existence, and go back for the turrets. Easy life. You will have to fly back down on occasion to shake off fighters that follow you up there, but it doesn't take long.
Nightmare Fuel: The disassembler, nanomachines reprogrammed to rip a target apart from the atomic level. Your normal Grey Goo scenario just makes more nanomachines. This one leaves behind a blood-red puddle of goo and a melted landscape. And then there's the sound. Just watch. There are repeated mentions that a disassembler attack turns humans into protein sludge. That means the aftermath could be harvested for food.
In the level where you go to the real Island Zero; if your first wave fails to cause crippling damage to the bugs' main production facilities, it becomes almost impossible for you to collect enough energy to clean the island. But the bugs have no similar problems. Well, not unless you abuse the fact they don't know you're there to knock out their oil rigs with a cloaked, flamer-equipped Puma.
Also the isthmus mission. Recycle everything. Create a wave straddling the isthmus. Inch forward. Create carnage, a little bit at a time. Advance to protect the recycling units. Use almost all the recycled bits to replace thrashed units. Repeat oh, maybe a dozen times. Then hope there's enough energy left for your main assault.
The escort mission is your first taste of the Species arbitrarily growing new units even if you've cleared the entire map. This in itself wouldn't be so bad, but the mission also forces you to waste two slots on static attack platforms and the final assault takes place on an isolated corner of the map surrounded by AA. You're pretty much guaranteed to lose your aircraft if you don't see it coming, and even then they might get themselves killed.