I have made Space Invaders successfully!, building it around a formation-based alien system with a CharacterBody2D player, grouped collision detection, and a Formation node that spawns rows of aliens, moves them as one unit, and steps them down and speeds them up as more get killed. Aliens fire back at random intervals, the player has lives with a brief invulnerability window after getting hit, and there are destructible shield blocks and a bonus UFO for extra points. I have integrated this with my original machine manager, so the game runs on the same flow as the pong game from before, attract mode when idle, countdown on start, and a continue system that spends a credit to keep a match going after a game over. Score, lives, and a persistent high score are all tracked and saved to disk.
I am now going to move onto a simple snake game and then maybe even breakout? please leave suggestions.