I definitely agree that this is an amazing and fun game the 1 and only real time you play through it, but feel the lack of replay value brings the enjoyment down. I do like the sense of accomplishment the game gives you and that though you can't die it doesn't make it any easier. Very creative design, and AMAZINGLY well done. It is like playing a painting at an art gallery.
For that reason I find the $15 reasonable. If you look at it as a piece of art more than a game. I was proud to pay for it because it means I'm helping promote a game like this and the idea. Without support original ideas die and all that remains is "Maddin XXIVIVIX" in our gaming future