http://www.gamasutra.com/view/feature/4078/the_history_of_defender_the_joys_.php
looks like my next game to make is choosen for me, although knowing me it will metamorphise into something different.
I might go for the original's retro look, Im not sure about the controls though
note - whilst defender is the coolest arcade game ever its not my favourite
controls are hard like I expected, with the reverse + thrust (though of course its not set in stone Ill use that in the final version)