The first time I played this I was so bored. It's a scrolling maze game where you dig holes to trap monsters. Ho-hum.
Then I cranked up the difficulty (to "difficult") and it was a revelation. Suddenly it was like a single-player Bomberman style survival game. All sorts of special items spicing thing up, including (you guessed it) bombs.
So what was looking like a D crept up to a C, and is not in B territory. Still playing...