I started work on my first "proper" fangame a while ago, and as of right now it's about a quarter-done. It's going to be a 100-floor platforming-only game. I also thought that instead of difficulties altering saves, they would alter spike quantities. Yes, I know it's not much more creative, but it's something.
It's not too good, imo... but I'm getting used to fangame design philosophies!