I agree that it would be nicer to have white background with the letters. Grey, to me, indicates 'unknown'. I have also run into a bug: There are some squares where I cannot set a flag. Right-clicking shows the flag, and it immediately disappears again. All squares where this happened were at the edge of the field among them all corners). Also, I would make the flag picture a couple of pixels smaller, so that it doesn't erase the grid lines.

I haven't got a clue what you mean with "open it with 'intro' ". Also, pressing 'p' doesn't seem to do anything for me. Can you really get out somehow? If so, I'm not smart enough to work it out...

You have two options: You can adjust your own speed slider (before export) to the slowest setting that still runs it nicely on your machine (before it starts to slow down too much), and then export as before. That should make it slower for everyone. Or you can uncheck the 'Lock scenario' checkbox in the Export dialogue in Greenfoot. This will give your scenario in the Gallery the speed slider and allow users to adjust the speed themselves.

The Hard/Easy switch is a nice idea, but I find the actual mechanism a little confusing: If it shows "Easy" IS the game on 'easy' now, or do I select it to MAKE it easy? In other words: I am not sure which way around the selection is.