Thanks for your feedback you two!

@cowabanga: yeah well that retro style was intended, so I'm glad that I seem to have achieve it.

@aztec: Thanks! You can do alot using the draw_ and bmap_ commands of the engine. All bitmaps that are used are created once on start up and then used for panels. Thus the bullets, the player and the enemies are panels. The environment is achieved using draw_line and the numbers, which could have been displayed using digits on panels too, are drawn with draw_text.
If I find some time I might tidy up the source code and post it in User Contributions, if anyone is interested.