Just gave it a go. Quite a fun game actually. My compliments to the author. Some feedback that may be of use :

1) Use thicker lines, preferably in a color that contrasts better with white (although it'll be fine if the segment width is 2-4 pixels)

2) Support for drag + snap-to-intersect/vertex UX rather than click only. I instinctively tried this first.

3) Some sort of progress tracking (local storage or user accounts even perhaps)

Anyway, great idea and a promising start!