Nicely done, I'm on level 11 and having a good time with it so far. A question and some feedback:

I've always wondered how people do level design for puzzle games like this. Is there a formula or is it just experimentation?

I think the feedback when sliding the penguin could be improved. Sometimes it doesn't respond at all and when it does it either goes or doesn't move at all. I think it would feel better for the user if the penguin slid with your finger but would pop back into place if you don't pass a threshold.