The code clean-up has also made me think that it wouldn't be *too* hard to add a multiplayer mode to this thing, which could be loads of fun. I'll definitely give it a try once the single-player version is finished.
Tonight I'm gonna add in the rest of the enemies. It's pretty quick to add them, but I'm guessing balancing them with the gameplay is going to take some time.
Will post screenshots in the next update.