Quite fun. I agree with mrgreenfur that by level 13 the fun started to drain out of it.<p>Comments:
1. Provide more justification for the mechanics. Why does the character have to dig arbitrary patches of ground? Why can't you cross your own path? (As pure game mechanic, it's fine but you created a story/world, so follow through with it.)
2. The key icon is hard to read. I'd suggest dropping the antialiasing and draw fewer "teeth."
3. As a player, it bothered me how power-ups (shovels and keys) cancel other power-ups without any indicator. I'd either want an immediate level lost message or be blocked from picking up something until the held item was "spent."
4. The levels don't build very gradually. They go from easy to hard with few chances to learn tricks that could be used to beat harder levels. That learning curve is what makes great games great, often.