Its a really good mobile game, surprisingly. I would have given it 5 stars but... I have a few problems with it. Later in the game, you can't upgrade as often as the money you receive never increases, probably 1 upgrade every 5-7 races where I am at. Upgrades don't feel like they do anything. The AI slows down or speeds up depending on how you play. It's great for passing the time, but I wish there was more skill or the upgrades meant something.