The original Infinity Blade was one of the first titles that showed what mobile gaming was capable of, at the very least in the visual stakes. Even with its somewhat grindy and repetitive gameplay, the ChAIR-developed title went on to be immensely popular, enough so to justify a sequel. That sequel is currently available, free, with a few simple clicks.
As OzBargain user "Innamura" notes in this thread, Infinity Blade II is IGN's free game for this month. After hitting up the promo page, all you have to do is click "Get my free game", which will generate a code that can be redeemed via the App Store.
Despite mentioning it's only available in the Canadian store, the code validated fine on my iPhone 4 and the download proceeded as normal. You also have until January 1 to use the code, so, yeah, plenty of time.
I always found the touch-based controls incredibly frustrating, especially on the harder battles where precision isn't optional, but it's a good bit of fun before you're fighting the desire to toss your phone at the wall.