Thanks for all your generosity, both for making games for us and - especially - for sharing the code.
As for the new game, I always enjoyed top-down racers like Nitro and Indy Heat, so something in those lines would great. The Amiga lacks a good OCS "Bejewelled-like", as many have said before me, so that would be great as well. I always found that with a cute, cooperative 2-player one-level-at-a-time game like Snow Bros, Pang or Rod-Land is were the old A500 seems to sparkle the most, so one of those would be great as well. A nice, fast-paced (50fps) shot-em-up is always welcome (being it horizontal or vertical). Fashioning a simple strategy game, like SimCity or Historyline probably wouldn't take much time, I think. The Amiga has a huge amount of platformers, albeit only a select few are any good, so a good, well-designed and two-button platformer will be welcomed. The choices are plentiful.
In the end, you can do whatever you want. We'll be grateful for it, regardless of what it is.