The idea is quite unique, the interface flawed, the gameplay rewarding, but the learning curve is very, very far from decent, when after very straight answered 15-Pipe you get 16-Dig where after several tries I can't get more than 5 free $. I still couldn't get past it so I can't know if it's very, very misplaced and should happen near the end, or if there are something around 20 levels missing between 15 and 16, but this is a huge flaw to the game, lack of save system being a close second.
So, as I suddenly can't by any way get past a certain level I have to leave this game unfinished and I'm afraid I won't be back without a walkthrough.
In 15, all you have to do is stall the proceeding water as long as possible creating curved path and deleting wall divisions after they're all surrounded - the idea is simple. 16 is a frustrating annoyance blocking the path to the rest of levels.
Why is it linear again? If I could play the levels in any order there wouldn't be a problem.