Thank you for releasing the source code. There is no need to put .class files into the repository. Of course, as usual, I don't advise you to use copyrighted contents without the prior consent of the copyright owners even for non commercial projects, rather use free artworks under open licences or create your own ones.
I've bought the full metroid fusion sprites from Nintendo BTW.
I will try to use as much open artwork as I can. The Samus (player character) graphics for example is copyrighted so you can play my game with it but unfortunately I cannot pay for all of you. The dimensions of the graphics files are however set in their respective filenames, e.g. player-left-40x40-1.png, see the pics/ directory.
Thanks for commenting.