That was really cool, and it's especially impressive considering it's the first game you publish!
I think the difficulty was good, not too easy but not so hard that you have to go through the levels 100 times. Also I'm gonna be honnest, the amount of levels was actually just right. It's a personnal preference, but I like jam games not to be too long :) (Although I'll admit the one I made myself is longer than what I wanted ^^')
Anyway, congrats!