The Iron Curtain, though not actually a weapon, was certainly jaw dropping to see in action. However nothing compares to the Kinetic Fireball Incendiaries, which at first just sounds too cartoony to take seriously, but then just sounds equal parts awesome and horrifying.
The idea is to launch lots of hollow balls of rubberized rocket fuel with a hole in one side, and light them on fire.. They become rocket-powered fireballs that bounce around inside the building, killing everything near them in the most cartoonish yet horrifying way possible. The thing is, the flaming balls don't actually have to hit you. The concept works something like a martini shaker; the reason the shaker cools your delicious drink faster than simply mixing in ice cubes is because they move around the liquid inside, cooling a higher volume in a much shorter time. With the KFI, you get essentially the same thing, except the ice cubes are flaming balls that raise the ambient air temperature to over 1000 degrees in seconds, not to mention knocking down doors and spreading the same horror throughout the building.