I just saw an announcement for this project on freshmeat.net and thought 
I would mention it here:

     http://lrnj.com

This fellow is developing a computer role-playing game (CRPG) with the 
goal of "... [making] Japanese accessible to people who enjoy anime or 
video games, and wouldn't otherwise learn it". I am just the kind of 
unmotivated individual that the author is after ;)

Have not had a chance to download and try it out myself. It is not open 
source, appears to be shareware. Available for Windows and Linux. So 
there you go.