IShoot was also the first app to pull me into playing games on my phone. The concept was easy to grasp; it's an artillery game in which your mission is to pick the right weapon and guess the correct angle and velocity to shoot at other tanks spread out on a mountainous, two-dimensional landscape. Though its graphics are quirky—among the places the tanks appear are Mount Rushmore and the roof of the White House—iShoot is obviously a low-fi production. But that's not a rap against it: Nicholas paid careful attention to the way a novice progresses through the game, and he tweaked the levels of difficulty to make it maximally enjoyable. My $3 turned out to be a wise investment: The game provided weeks of fun—I fought tanks every chance I got, progressing from "easy" to "extreme" difficulty, growing bored only when I'd become good enough to beat every level.
Many of the best games for the iPhone follow iShoot's model—they're imitations of classic titles that have proven successful on other platforms. A couple of months ago, I downloaded Fieldrunners, an iPhone version of the tower-defense games that have long been a huge hit on the Web. Tower-defense games—in which you build elaborate mazes to prevent swarms of enemies from making their way across your screen—are notoriously addictive; the most popular Web version, Desktop Tower Defense, must have reduced global productivity by at least a few percentage points when it launched in 2007. (I missed a couple of book deadlines because of it.) Fieldrunners has all the addictiveness of that game, but it produces none of the guilt. Because I played it in stolen time—away from my computer, where I have other things to do—I didn't feel bad about the weeks I spent trying to beat it. I quit the game only when I made the terrible mistake of searching the Web for hints; I found a foolproof maze design that gave me a high score every time, rendering the game unfun.
There is no evidence that the iPhone has hurt the sales of traditional handheld gaming systems. In April, Nintendo released the DSi, its latest portable game system, and sales have been through the roof. But at least part of the interest in the new device has to do with a feature that Nintendo copied from Apple: an app store. The DSi connects to an online marketplace through Wi-Fi; games go for a few dollars each, and, as on the iPhone, you can play them instantly. At the moment, the library of available games isn't huge, but the DS has a large fan base, so you can expect game developers to build many titles for it. Still, the DSi offers casual gamers like myself little reason to switch—after all, it doesn't have a phone (even a crappy one).
My latest iPhone gaming habit is Strategery, a beautifully designed version of Risk. Once again, there's a simple premise: You take over a map by beating neighboring countries with rolls of a die. But developers have built startling artificial intelligence into the game's computer opponents; when you set the difficulty high, they anticipate and block your strategy with ruthless efficiency. It's nerve-wracking and often seems impossible—though every time I lose, I want to play again. Eventually, I'm sure, I'll get tired of it. But the App Store is huge and the games are cheap. In no time, I'll find something else to entertain me in the checkout line.