1. More than one mines in a square - the "cluster" part of this game.
The game model (Sweeper.java) was designed with this goal in mind. As a result without much specific coding it's already playable via the terminal interface (SweeperTester.java). Check out the CVS! The graphical part should not take long once I have the icons from a friend.
2. Full solver.
The solver can only do single square analysis right now. I have some algorithms in mind for the more difficult parts but it will take some time to code. Well, turns out single square analysis already does a lot!
3. More options.
Such as generating safe field such that you never have to guess. I'm not quite sure how to do this: maybe finish the solver first and run solver discreetly to find choke points (and reconfigure them), or maybe find some way to identify choke points locally.
4. More boards.
I'm not really interested in triangular or hexagonal or other weirdo boards. If we are going to do it, the model support for such boards should be no problem. The hard part will be the graphical interface - we can't use JButtons. We'd need customised painting and mouse tracking.