The more I see of this project, the more things come to mind. Levels where there are stationary objects that must be destroyed and each slowly spawns enemies until destroyed. A boss level where a boss is fought once you defeat it's stationary objects which spawn enemies etc...Bosses could stand out like the Asteroids and even throw asteroids at you! There could be vortexes that transfer an object from one side of the sphere to the other, or just suck the ship in to destroy it if you don't avoid it. Warp gates, meteor showers (avoid falling objects while defeating enemies) There are just so many things, over time which could be added and modified to really structure this into the most amazing shooter of it's genre. Who knows where it will ultimately go. This will be fun to follow as it already looks awesome!