In Blue Defense!, you are the planetary defense cannon tasked with defending your blue world against an endless onslaught of red attackers. The odds are against you from the start; your attackers come in droves from all sides, while you can only fire straight up. Luckily, "up" is relative. By rotating your device - often frantically - you can change "up", effectively aiming your cannon in any direction you please. It's a mechanic that works extremely well for the game, making brilliant use of the iPhone's accelerometer as a primary gameplay mechanism and providing a gaming experience not dissimilar to playing a game on Nintendo's Wii.