Heelo Dave,
Here are a few suggestions to enhance the game, pick only whatever you like from my proposals!
Suggestion #1Put a timer, save high scores for the 3 Easy, Medium and Hard levels.
Make sure to stop the timer if the player exits from the game and to start it again when the player comes back.
Suggestion #2 (maybe the most important one)Offer another more user friendly way to control the flagging of a cell.
This could be:
- either a stroke of the pen from the target cell to another cell
- or a long pen tap on the target cell would turn the flag on, a quick tap to turn it back off, another quick tap on a non flagged cell would undiscover the cell
=> having chosen to work with images and no more buttons (as in your original proof of concept) opens this kind of great enhancement
Suggestion #3Put a dramatic bomb sound (with PLAYWAVE) when KABOOM!
Same thing with a great relief song when not KABOOM!
Offer option to turn sound off, whatever the Game system setting is.
Suggestion #4Your application is not only freeware, it also is open source. Worth mentionning it in the About box, this is a very nice offer from you.
Suggestion #5What about a nice bomb image?
Even an animated one? (a little bit like I did in the Matches sample application with burning matches)
These are just proposals.
Your game is already a must have as is!

Cheers,
aldweb