Very good game, it gets quite hard further you progress and you need a bit of time to understand how the puzzles work but once you understand it, it gives you a lot of satisfaction when you each level.
The only issue I had is when I accidentally made a wrong connection I was losing all of the progress. I worked around it by making screenshots of my progress and redoing everything back to a moment where I made a mistake, but it would be nice if we could just delete connections between the numbers :)
Besides that graphics are extremely well done and the music is very soothing, just perfect for this type of game.