Of course all roller coaster games have their twists and turns, but Off the Rails (US$1.99) lets you build a complex roller coaster in real time as you steer. As you move your iPad or iPhone you see the roller coaster being constructed in front of you. Of course, moving around wouldn't be all that interesting, so the game presents targets for you to hit. An added challenge is that the game observes the laws of motion and physics, so you can't twist and turn without some penalty.
The 3D graphics are great. I got enough into the game that I felt i was really in motion. You get to choose from 14 different vehicles, and there are more than 75 targets or objectives to the game. A young player could learn a bit about physics while having a good time.
The graphics are very smooth, and the sound effects are well done. You can save the coasters you design, and your movement is steered by tilting your iOS device in different directions.
I don't usually get too excited about games, but this one is unique and graphically compelling. It has a high repeatability factor, and It's a nice variation of the usual coaster games. I found Off the Rails more involving and more fun than the others I've played.
The game is aimed more at kids than adults, but this adult had a good time.
Off the Rails requires iOS 7 or later. It's optimized for the latest iPhones and it's a universal app.