So it is getting very close to the end of the js13k contest and I have essentially finished my puzzle game. But I had to do some user testing to check the game balance and cross-device comparability.
I put the near finished product in front of 4 players who had never seen it and let them play (and fed them breakfast and coffee).
I think the test went really well and people seemed to enjoy the experience. It is clear that people can figure out how the puzzles work and also that the progression of difficulty is fairly sane.
I also established that I have succeeded in meeting my original goals of: a) '1- 2 hours of game play' and b) 'being reasonably challenging for most adults'.
I also got a few important UX issues regarding the placement of controls out of the testing which will involve a few small changes.
Two days to go; current size 10.7kb; so far so good.
EDIT: I didn't want to show the game so close to completion but here is the version used to user test with.