A very promising start! Despite the graphical limitations, you manage to pack a lot of detail into every sprite and tile, while still keeping them clearly readable. The core game loop seems like it will be fun too, once there's a bit more variety (I'd like to see the various monsters differentiated in some other way than just strength). Have you considered inverting the colors for the above- and below-ground sections? (dark on light, like the background of this page, vs light on dark, like the game itself)

Good work!