I tried to prog Baku Baku Animal (Sega Genesis) with Gosu, and this is it:
http://www.youtube.com/watch?v=1Mf-WMmqrg8This video shows the game only at half speed due to fraps.
In my opinion it's far from being complete. I coded it in Ruby at first in order to get to know ruby, without smooth animation, but then turned to cpp, as it seemed easier for me.
BTW, coding did not take longer than a week. Drawing did.
pythong