Got the very basic gameplay mechanics of a Space Invaders type game up and running fairly quickly. Only needed to do minor changes to my old Pixel Raiders code as I had made the collision between the game boundaries needlessly complicated.
Next up I'll look at getting some more enemies, explosions and maybe a scoring system in place. I'm hoping by the end of tonight I'll have all the basic elements in and working, so I can spend tomorrow working on the roguelike part of the gameplay and super weapons.