Today I created the core gameplay loop for the game which included:

Prototyping the several generators you're tasked to defend

Prototyping enemies, enemy spawners and their respective behaviors

A system for shooting, reloading, damaging enemies, ammo, weapon properties (will later be able to upgrade)

A system that determines when a wave of enemies spawns and handles wave begin and end events

Being able to repair generators that have been damaged by enemies

I also got carried away and created three wormholes that take you to three separate off-world locations where you'll later go to buy upgrades. I currently have the Moon, Mars and Europa (moon of Jupiter).

Fun day!