I am still not sure what I am going to do, but I did have this idea:

I might make a game similar to Gyruss, where you have to rotate around the centre of the screen firing down towards the centre, but all graphics are vector graphics with glow.

Maybe, there will also be 'tracks' that the player ship has to move along as it moves around the centre - maybe just left right, but might have in/out too...

At least if I do this, I won't have to worry about creating too many graphical assets - each object would just be a bunch of lines

cheers,
Paul