Hey everyone, I'm playing around with the Gosu game library now. (no  
pun intended)
It's not bad at all. The tutorial makes some things pretty self  
explanatory. (though it could use some more details, but what  
tutorial couldn't?)
Anyway, I highly recommend it, but if you're a complete beginner with  
Ruby (especially completely new to programming) it might be a bit  
much at once. But maybe not. It's pretty straight forward stuff.
I'm looking forward to soon trying out 'rubygame' as well and  
comparing the two.
I'm betting that Ruby may well take on Python in this department if  
more people give Ruby game development a try!