In addition to making the game run better and allowing it to run on your large HD TV, there are also some changes to the gameplay. There is now the option to enable an analog thumbstick control, the ability to shake the device to activate your melee attack, and there are also some cosmetic changes as well as the usual bug fixes. The update for Rage HD is available now on the Apple App Store. If you don't have the game yet, you can purchase it for $1.99.
source: Ubergizmo