I'm going to go out on a limb and say you've probably played a game about shooting zombies. In fact, you've probably played several of them. They've practically evolved into their own genre, thanks in no small part to the mainstream success of titles like Left 4 Dead and Dead Rising.
As an avid fan of the House of the Dead series, I approached House of the Dead Overkill: The Lost Reels with a slight feeling of concern. It's an iOS and Android port of a game I thoroughly enjoyed, and it's always worrisome to see a console game get adapted for smartphones and tablets. Now, having played the game for almost 20 minutes, my feeling of concern has turned into one of anticipation.