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The concept behind Cube Runner is simple. You're a 3D arrow that we can assume is some form of plane and you're objective is to not hit the cubes that are scattered out all over the landscape. That's it. There's no lasers, end boss, or power ups in this game, but that doesn't mean it isn't addictive.
The game takes advantage of the accelerometer completely, making this something you can't really play discretely. By tilting the phone to it's sides, your plane begins to lean in that direction. You're moving at a constant speed that you can't control throughout the entire game, so you don't have to worry about tilting it forwards and backwards. Cube Runner isn't exactly a graphical masterpiece either, as it's simple solid color 3D objects that you try to avoid on a gray ground with a blue sky. Considering pretty graphics wouldn't add anything to the game, there's nothing really lost in that regard, but it's not the nicest looking free game on the iPhone.
You get one life in Cube Runner. When you die, you start over. The issue with that is your points are based on how many seconds you've been alive. So if you manage to not hit a single cube for 10 minutes and you die, you'll need to have the patience to actually play the game for longer than 10 minutes to beat your high score. While this doesn't annoy the casual player at first, once you spend any amount of time over 2 minutes playing the game, you start to get frustrated with the fact that you have to commit over 2 minutes for it to even be worth playing.
Don't expect a ton out of this game and definitely don't delete it. Throw it on to your last page and play it when you've got plenty of time to kill. After all, it is very addictive.