Extraction: Project Outbreak is a recent title from Chillingo that's an interesting mix of shooter and what's essentially real-time strategy. You control one soldier as you fight through a series of missions, and the control scheme is pretty interesting. You touch on the screen to move around from point to point, and then you drag across the screen to line up shots on your zombie enemies.
The game is a real balance of movement and gunplay, as you try to move and position yourself to keep from getting hurt even when you're surrounded by the bad guys. Action ranges from tactical to frenetic, and lots of upgrades mean that as you go along, you can make both your soldier and his weapons better. There's a full singleplayer campaign to play through, and a few different modes to check out and mess around with.
Extraction is fun. The action is simple but entertaining, and the graphics range from above average to really great. It's a great title for just sitting back and murdering some zombies with, and while it runs fine on the latest iPhones, it looks and plays better on the iPad. The game's available on the App Store right now for 99 cents, with in-app purchases available for extra in-game XP or money.