I’m giving this game 1 star simply because of the significant battery drain, which I think the developers need to address. Even when set in HQ mode (go to settings in top left corner) this app drains 25% of my battery (iPhone 6s) in 5 minutes and killed my battery after playing for 20 minutes! I would like to know why and, more importantly for the app, would like to see it fixed.
Otherwise, the game provides a great mental challenge and plays very smoothly. The graphics are calm and pleasing. The movement (rotation) of some pieces can be frustrating at first, but not overly bothersome after figuring out the “technique”. Overall, this simple game is a time-drain that is worth the $1.99. Unfortunately, is not worth the battery drain.