These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Hostile Waters Antaeus Rising
Game Breaker: Puma + Cloak + Flamer = You win. Always. 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. 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. Even when the enemy respawns them, you just need to fly a plane over as a spotter, then rinse and repeat.
Hell Is That Noise: The hellish chitter-whirr-animal noise the Species units and buildings constantly emit. On the other hand it makes them very easy to detect, even if they aren't appearing on your radar.
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.
That One Level: 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.
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.