Good game, but quite a few problems, it isn't very clear, and i don't know whether this was just for me, but on Google Chrome, you can't scroll around the screen, so i swapped to IE ;P
Anyway, i've also got a weird bug where i spawn on the 5th mission, "Abadoned Mineshaft" with 0 Gold, everytime, which makes that level impossible to finish, making the storyline also impossible.
May also want to add some better music, such as some action music, or maybe each level having its own theme, this may be based off Minecraft, but remember, this is your game, you can change what you want to.
Also, another problem i encounter alot, is when i get a bonus on some mission i'm about to fail theme when i get the added gold, so it is completely lost. So perhaps that should he changed to + however much gold. Next mission. Or you can choose when to cash them in, with a limit of only cashing in a few at once, otherwise the later missions could become easily dealt with.
Aswell, the scrolling Jams alot On IE, and refuses to move until i've mashed all my arrow keys for 5 seconds, wasting time in the first phase.
That last thing might just be my keyboard, but i thought it might be worth mentioning in case it isn't.
Good game, Very interesting concept. Could become a very sucessful one with a bit more work.