Thank you for your feedback.
I added casual mode because I got feedback from jugule. He got to the point that hard to-control game is not fun.
You are also right about the gameplay at the end. I definitely will take your advice.
About themes, I predicted that most of the entry will be platformer. So, I decided to not use gravity and ground to make my game a difference. It turned out it felt like not fit the theme as you mentioned though.