Alien Swarm is a 4-player co-op shooter released free by Valve on July 19th. It is a full remake of the Unreal Tournament 2004 mod of the same name, made by the same development team. It is best described as a twin-stick shooter, as, with the top-down camera angle, the WASD keys are used for movement, with aiming being handled by the mouse being pointed around the player character. Basically the crux of the game revolves around a team of Marines sent into an off-planet base to eliminate a swarm of aliens that has infested a human colony.
Different classes have different weapons and skills made available to them, with a good variety of class selection being essential to the completion of missions. More weapons can be unlocked by earning achievements and experience through gameplay.
Having played a handful of missions, I can say that while it’s hardly Game of the Year material, you’re certainly getting a lot for a free game, as it is fully customisable, coming with the Alien Swarm Software Development Kit (SDK) absolutely free as well. This leaves plenty of scope for new, totally converted missions that have little in common with the original game. However, even without the SDK, there’s still a myriad of things you can do with the Developer Console, activated within the Options menu, such as turning on the Left 4 Dead “AI Director” to oversee the swarm spawning patterns, turning the game into first-person mode – defeating the purpose of the game’s structure – as well as a host of others (which you can see in this thread on the Steam Forums)
It’s quite fun overall, but as with Left 4 Dead, I feel that once you’ve run through the missions a few times, the repetition can seem to get to you, and you can nearly predict where aliens will appear from without having to use the movement sensor on the map. Most of the enjoyment here I think will be the mass of user-generated content that can be added onto the game, much in the way Garry’s Mod operates. Good place to start looking for new missions and maps would be the SwArmory and ModDB, although at this early stage (4 days at the time of posting) there are very little full releases in terms of mods, while people are still getting used to the editor and trying to get the best out of it.
You can grab the game here, but as with all Valve games, the Steam client is required to play it.