Thank you! :)
I appreciate the feedback. Art has always been one of my worst aspects when it comes to game development so I always try to keep my game's graphics simplistic. I do agree that I could have added some more animations and lighting/shading. I did try to add an obstacle that had a simple animation but I didn't think it turned out that great in the end so I removed it. It would have been some kind of geyser or gas vent that periodically burst, blocking the entire shaft for a short while. I felt that the animation needed to be very clear and obvious so as not to feel unfair and in the end I didn't think the animation achieved that.
Anyway, thanks again for the feedback! I'm glad you enjoyed it.