I keep thinking heavily about trying my hand at a Cave Story hack since I've been playing the Wii version after a good two years of making myself not replay the game anymore so it'd feel as fresh as possible when it came out on Wii. I'm realizing that that was quite silly of me and when I'm done with all the Wii-only content I'm going to start looking into hacking/modding. This is one of my favorite games ever and it's like I have this subconscious urge to do something really special for its community to 'apologize' for not being a part of it at all for too long, or something.
Of course, aside from the easiest game hacking tool ever created in the history of mankind, Lunar Magic, I haven't done any real game hacking except for some Mega Man 2 and 3 stuff, and a little bit of Zelda Improvement--and with none of these programs have I actually completed a hack, even enough to put up a beta version or demo. However, I feel very strongly that with my renewed super-interest in Cave Story I'd be able to stay focussed enough to really see it through.
I have a couple ideas off the bat. One would be a simplistic but atmospheric take involving mostly dark, music-less rooms with only a specific style of the music being used, such as "Zombie" for bosses. I'm thinking of the story being told in the pop-up text boxes i.e. how Ballos' story was told in the Sacred Grounds in the original.
I've also got the greatest idea ever for a comic hack featuring Mahin as the playable character. That'd be my greatest masterpiece if I managed to pull it off.