Added in some nasty little Interceptors for a bit of variety. They are more aggressive on the way in but fire less on the way out.
Difficulty level code is implemented, at least in the gameplay - still need to add the menu options. At the moment it ranges from Space Slug through to Impossible.
A couple of screens showing me getting into a bit of bother:
I have uploaded a video of me playing on Insane (second to hardest):
At the moment, I can't beat it without losing at least one life. Need more practice!
The final game will have the option of an energy bar (shields) and for the truly dedicated arcade headcase a 'Hardcore Mode' with single shot instadeath.