I love the idea of being trapped in a mine - something very cool about what might be hiding down there and the claustrophobia of it all. Maybe next time, you could make your map smaller and focus on bringing out a few more of those fun 'finds' and details, like with the body at letter at the start!
The walk speed was also a bit too slow for such a large map. I hope you continue with the idea though and I'd love to find out what's at the bottom of the mine!