Alien invasions are perfect video game fodder. They provide a fantastic backdrop for amazing heroism and allow the use of neat sci-fi weapons and gadgets that might otherwise seem out of place. Perhaps the enticing aspect of this scenario is the underdog factor. Except for a few rare occasions, humanity is almost always the ones who are being overwhelmed by the advanced alien weapons and powers. It's much more exciting when humans can come up with a way to blast aliens to pieces. Everyone loves an underdog victory, and 0 Day Attack on Earth is a game built entirely on this concept. It doesn't have much of a plot, but it focuses entirely on what makes those sorts of adventures exciting: pilots in inferior machines using their skills to overcome a seemingly unstoppable alien foe.

0 Day Attack on Earth is an overhead shooter, and the controls are really simple. You pick an aircraft of your choice and are instantly thrown into the battle. The left analog stick controls your ship's movement, while the right chooses the direction you want to fire. The right bumper will drop a bomb that destroys all enemies nearby, while the left allows you to temporarily boost in a certain direction. These are all the controls you need to play the game, but there are some interesting mechanics involved in 0 Day Attack on Earth. Every enemy you kill drops a green orb that increases your score.

These orbs also have other uses. For instance, they slowly refill your ship's health meter so you can remain in fights. More importantly is that these orbs also power up your ship. Each of the different types of ships has a unique three-tiered weapon system. At level 1, it's a puny machine gun, but as you pick up orbs, you'll level up the weapon. Higher-level weapons vary depending on what aircraft you're using and can be either a spread of multiple machine guns, homing rockets, heavy cannon shots or flamethrowers. At level 3, weapons usually gain more attack power and unique attributes. My personal favorite was a helicopter that gained a flamethrower at level 2 and a second rear-mounted flamethrower at level 3, allowing it to become a whirling fireball of death.

0 Day Attack On Earth's missions are structured rather simply. You're dropped into the middle of a furious air battle over one of Earth's cities, and your goal is to eliminate the enemy leaders within a certain time limit. It sounds simple enough on the surface. Arrows on your HUD and red dots on your radar show the exact locations of the enemies you need to kill. It can be a bit challenging to kill them, but if you focus on them, it isn't too difficult. There are also tons of alien machines scattered around the levels, just waiting to be blown to pieces by your weapons. Destroying enemies increases your score, and the more enemies you destroy, the higher your score. Simply winning the game in 0 Day Attack on Earth shouldn't be your overall goal; in old-school arcade style, you're attempting to get the highest possible score within the time limit. This means that you have to destroy the leaders and as many of their minions as you can. You generally have an excess of time, but it still involves careful management of your abilities. Spend too long farming weak enemies, and you might not have time to break through your enemy's defenses and take out their leader.

Enemies in 0 Day Attack on Earth come in all shapes and sizes. Different enemy fighter crafts have different tactics: fly around and try to smash into you, fire lasers, crush you in a vise, teleport behind you for an ambush, or even latch onto your ship and attempt to self-detonate. These enemies are dangerous because of their numbers and not their individual attack power, but you also earn you very few points for destroying them.

In order to get a ton of points, you have to attack the enemy's big assault crafts, which take up a good chunk of the screen and have tons of weapons and strong defenses. You have to pound on them for a bit before they explode, but you get a lot more points in exchange. These mid-bosses come in many forms. Some are tripod walkers à la "War of the Worlds," while others are flying snake monsters or weird flower-like enemy spawners.

The deadliest units of all are usually the leader units. These units are large and often take up most of the screen, and they can withstand bullets with ease. They're also powerful attackers and can launch swarms of bullets, tentacles or other weapons, forcing you to dodge or be destroyed. The leaders are actually the most interesting units, and for good reason. While they are usually dangerous, every so often, they'll go into an attack pattern that's deadly but easily dodged. If you back up, you'll generally keep yourself outside of their range. The only problem is that this puts them outside of your attack range as well. If you want to easily avoid their attacks, you can't damage them until it is over, wasting precious time. Each enemy has holes in their attack patterns that you can exploit to continue damaging the unit even when they're going all out with their attacks. The problem is that this puts you at much greater risk of dying. Getting caught in one of these swarms is almost instant death, turning the game into a pseudo-Gradius, where you are a moment from death at all times.

If you play 0 Day Attack on Earth in single-player mode, you're aided by a group of NPC planes. These planes can't be killed, but they also can't upgrade or be commanded, so they're of limited use. The real way to demolish the enemies is going to be in co-op mode, which allows you to play online with other gamers. It generally follows the same basic rules as the single-player game, but it also has a few twists. All the units share lives, so if one dies, all players lose a life, but death isn't an instant game over. Once all your lives are gone, you get "frozen" instead of killed, so you're prevented from doing anything unless one of your allies shoots you free or you wait a lengthy period of time. If all allies are frozen, the game is over.  Like the single-player mode, this plays into the goal of earning a high score. You can generally avoid getting a game over with careful play, but every moment wasted on a frozen ally is one less second you can use on earning high scores. The game will also feature competitive multiplayer with traditional Capture the Flag and Point Capture modes, where two teams compete to either capture the opponent's flag or hold certain areas for a period of time.

0 Day Attack on Earth has the makings of a great arcade game. It may not have a deep plot or interesting characters, but it perfectly captures the feel of the "Independence Day" movie. Zooming through the enemy defenses and trying to destroy as many foes as possible is quite exciting, due in no small part to the way the scoring system works. The game is designed in such a way to encourage you to take risks and play offensively, as each wasted moment brings you closer to running out of time. It's an interesting mechanic that even pushes cautious players to take risks. The online mode looks to be a well-made cooperative game for players of all skill levels. The freezing mechanic prevents high-level players from being held back by novices, while still letting them play together with their friends. Competitive multiplayer gives those same friends a chance to tear each other apart.  All in all, 0 Day Attack on Earth is shaping up to be a solid arcade shooter. It might be disappointing to those who buy Square Enix titles for their plots, but anyone looking for an addictive old-school arcade game will find a lot to like here.