Controls are simple. You move back and forth by tapping the arrows on the left side of the screen and shoot by tapping the red fire button on the right. As you might imagine, the game rewards furious tapping.

As with the original Space Invaders, a mothership will occasionally hover across the top of the screen. And your position is protected by three (instead of four) large blocks that the invading ships (and you) gradually blast away. Purists may blanch at the fact that those blocks regenerate, but you need the protection as the aliens here shoot more often than they did in the original game.

Aliens Invade might also appear to be less challenging than its ancestor. If you collect enough power-ups, you can sit out in the open with your shields up and blast away at UFOs with homing missiles or exploding ordinance while taking incoming fire with impunity. But don't be deceived. The power-ups don't last long--you can watch each power-up's draining supply at the top of the screen--and some, such as the laser beam, are pretty rare. Also, those UFOs move a lot faster than they did in 1978. That's why you need so much more firepower.

Drawbacks? At least one, and not a small one: The controls get a bit sticky, especially if you're in one of the corners of the screen. But I've also noticed small--but occasionally deadly--delays in response from the controls. You have to double-tap to make sure your gun platform moves. When I've died in the game, it's usually because I've been stuck someplace and the controls haven't responded.

The game does not require a Wi-Fi, 3G or EDGE connection unless you want to share your high scores with the wider world. The latest version incorporates OpenFeint, a social networking platform for the iPhone geared toward the burgeoning gaming community. OpenFeint lets users set up gamer profiles, post messages and chat in games. The add is optional--you aren't required to turn the feature on, it only works if you're connected to the Internet, and there isn't much of a reason to chat with anyone in this single-player shooter anyway.