I got stuck on the second level of the tutorial. Here's some thoughts:
During the first level, some of the Tutorial dialog pages were blank.
I wasn't really sure how the Block towers changed the nearby arrows. Sometimes they would add arrows to adjacent blocks and sometimes they would remove it. Never figured out a rhyme or reason to it.
In stage 2, wave 1, I placed a block tower in the top right corner and then a tower to the left (top middle block). This created a path from the start to the goal tile, and the instructions said that the monster needed to go through 3 tiles (including S / G). The monster went through 3 tiles (S, in between S and G, and G) but I was informed that it didn't count because the monster still had HP left. I think that the S tile isn't getting counted in those '3 tiles' - the UI should be updated to reflect that.
I think that casting this as a Tower Defence game is confusing the terminology a little bit. Are we trying to get the monsters to the goal? (If so, then why does it matter if they have HP left?) Finding a different theme or just different words would clear things up. For example, I think you could replace HP with "Steps" (as in "this monster can take three steps before it dies") and things would be much clearer.
It's an interesting idea for a puzzle game. Keep on game dev'ing!