Hi Jason! Thank you for the feedbacks.
I agree with you, there are things that need to be more dynamic. I'm currently working on stages. In the future version stages will be generated by specific templates made by myself. I mean, numbers will be always random, but the layout of the stages will be always the same, so that I can make the puzzle fun to play with. I've also added a new item:
You have to put the right number in the adjacent cells in order to free the one that is locked.