Just beat this level. I found it extremely fun! I would say my skill level is pretty much beginner. I have been playing SMW hacks for about a month now. This felt right in my comfort zone. A good challenge but clearly beatable. I think removing the checkpoint could make it a bit harder but still a doable level for someone a bit more intermediate.
The "4 shell" thing was my favorite part. It took me a couple minutes to figure out what I was supposed to do but once I did it was awesome (I don't think you can make this any clearer, the coin indicators were great). I also liked how the mole trolls you before getting the checkpoint but then is also needed doe the next section.
Really my only constructive feedback is that it felt a little short. With that said, the shortness is also probably what kept it in my skill level. If you made 4-5 levels like this I probably wouldn't have this complaint. I thought the graphics were a bit simple but very clean.
Overall, great work! I will definitely play any other levels you put out.
Let me know if you would like any more specific feedback.