Fantastic concept. I'm a big fan of how you reframed and renamed the Havoc mechanics to match your genre. I tried to do some of that but just couldn't get there. Even though the mechanics of the engine are havoc, the way you presented them felt like they belonged to this game.
The characters were excellent. I especially loved the mutated kangaroo, alien, and bomb shelter hive mind. The concepts feel unique without feeling ham fisted which I think is an issue I ran into in my game.
Lastly, I was a big fan of the mission structure and how modular it felt. It felt easy to envision someone building their own missions based on your template even though that's not technically in the scope of your game.
Great job pulling all of that together for what feels like a really well rounded and refined game.