Alien Swarm follows a squad of four marines as they clean up an infestation of the Swarm on a mining outpost. Unlike most games and movies that follow this same formula, the military knows about the Swarm, so they are prepared for what they have to do. There is currently only a single campaign, which follows the progress of your squad through the colony and to the inevitable nuclear destruction that will punctuate their journey. That's about it for the story, and frankly, we don't really care. It's a free, top-down, co-op shooter, after all.

The presentation of Alien Swarm is impeccable. The graphics have the smooth feel that Team Fortress 2 has, rather than the muddy textures of the original game. It's dark and spooky, but not by sacrificing legibility, which a lot of games seem to do. The animations are all incredibly well done, the environments are interesting, and the art has a distinct campy science-fiction feel to it. The sound is also excellent, with appropriate sound effects and music permeating the game. However, it is extremely poorly optimized. You will want a system above the recommended settings if you want to play smoothly. Framerate stuttering and audio lag are major issues for lower-end systems.

The gameplay is fairly simple. You must progress through a series of levels, each of which is part of an overarching campaign. Each mission has a set list of objectives, such as activate the reactor, burn all of the Swarm eggs, or destroy a pipeline funneling the Swarm around. These objectives are usually pretty self-explanatory, but in case they aren't, the game does keep you from starting a mission if you are missing a requisite marine. You can also lose a mission if a certain marine dies, such as if a Technician dies before you completes a Technician-specific objective.

There are four marine types, with two possible marines of each type being present on a team at once. They are:

• The Officer, who is the standard grunt of the outfit. He is the only character that can carry the Vindicator, a strong semi-automatic shotgun that deals devastating damage to the Swarm. He is best serving as a mobile trooper, assaulting all threats at all times.
• The Heavy, who is the big guns. His special weapon is the Autogun, which is much like the gun seen in the movie Aliens. He's a powerhouse of damage, chewing through aliens like crazy. Unfortunately, his weapon of choice also chews through ammo and only holds two clips. As one would expect, all of his stats and weapon specials are related to this damage-dealing role.
• The Medic, whose role you can guess. The Medic is the only class that can use the medic pack or medigun, making it essential to the survival of the team. The Medic is also the only one who can prevent a teammate dying of infestation, as healing is the only way to survive it (except for electrified armor; more on that later).
• The Technician, who is the only class that can hack consoles. The Technician is pretty important, as many of the missions have locked doors that require opening via the Technician's skilled hands. His weapon is the prototype rifle. It doesn't deal as much damage as other weapons, but has the benefit of lock-on capabilities as well as the capacity to fire shock grenades to stun enemies. The Technician is best used in a role similar to Officer: mobile kicker of asses.

While the classes are important thanks to their unique weapons, there is also a massive stable of alternate gear to carry with you. Every player can carry two primary equipment choices and one secondary choice. Primary choices are things like guns, deployable resources, and sentries, while secondary choices are things like flashlights, homing rockets, and armor. As most of your potential choices have no restrictions, players can build their character how they want. Want a flamethrower wielding medic who heals her teammates and explodes enemies with rockets? Sure, why not! Or how about a shotgun-crazy Officer? All is possible with the modularity of the inventory system.

Those addicted to progression will be happy to know that, unlike the original mod, progression is global. The game keeps track of your stats and grants experience as you complete levels. Gaining new experience levels means getting new equipment to use. The current maximum level is the paltry level 27, but like the latest Call of Duty games, you can give up all earned levels for a "promotion," starting you at the beginning and giving you a special marker next to your name. There are also achievements, and note that you can earn achievements multiple times: all times after the first merely add to your experience total instead.

Alien Swarm is one of the best Freeware games to come out in recent memory. It's a big-budget project by a developer many PC users adore, and it doesn't let down. There's a few minor issues, such as bad optimization and only one campaign, but beyond those, the game is virtually spotless. You can get the game through Steam. Remember that you need the Steam client in order to play Alien Swarm, especially since your stats are recorded and saved using the Steam Cloud system.

For another look at freeware games, take a look at Joystiq's Free Game Club weekly feature!