Yes, it was unclear that it is possible to rotate the blocks. I think the design would be more clean if it was not possible to rotate the blocks, but it might get harder to make a lot of levels. One idea might also be to hint after a while with some gray lines that the blocks should be rotated.
I think its possible to make a "rotate towards angle" to get a rotation effect.
The graphics is very nice, but its a little confusing when all the blocks are the same color. One idea might be to have some slight variations of tone or shades, just to make them look a little different.
I really got stuck on level 10:2, I'm not sure how the difficulty are suppose to be, like if all levels are going to be the on a fairly equal level or if you want to mix harder and easier once, If you want to mix them, it might be an idea to indicate the harder once clearly.
It would also be cool with none-linear level progression, but I'm not sure if it "sells" on mobile.
I like the touch of how the screen scrolling down when you complete the level. Would be cool if it was some kind of effect, maybe water inside the darker area when you complete the level