One of my favorite mobile games, just a really cool concept with good music, and memorable enough that I came to re-play it 5 years later. No ads, instead opting for in-app payments for additional modes and checkpoints. While a lot of people have issues with not having checkpoints, I'm fine with the tradeoff. When I was learning to play and failed, the game kept me interested so I didn't mind restarting. Mastering the game such that you can play the whole thing from the start feels really good.