Imagine standing around with your mates as one of them is hacking into a computer. You know they'll be coming for you soon, it's more a question of when and more importantly from where! You'll all cover different angles while you special weapons expert sets up a hefty automated sentry turret, it's reassuring sounds bringing only small comfort to the onslaught that's about to occur.
And then you hear the sound, the quiet but unmistakable double beep as a dot flashes suddenly on your movement sensor and without any further warning one is upon you! A stinking alien with it's jaws wide, poised to strike and it's only by luck that the sentry gun is pointed your way as it instantly piles a small but powerful salvo of hot-lead-death directly into the xeno's mouth while you stand, dumbstruck and panicked.
After that moment however you've remember where your trigger finger is as the wave approaches, a moving carpet of unreal bio matter spreads towards you. You and your team don't let up, as the wave starts to encapsulate your team desperation hits and you notice that the sentry gun, the only thing keeping the sides even and in balance is running out of ammunition. And finally, it's only when sarge decides that a few well placed grenades are in order that the wave subsides, relief hits you and you hear the audible sighs over the com system.
That's pretty much the gist of the game for me and pretty much sums up my experiences with Alien Swarm. More specifically it's a top down shooter, in the style of Alien Breed or, going back further, Gauntlet and is a 4 play co-operative game from no less than Valve Software.
It's been out for a few weeks now and they've already updated it quite substantially, including new features such as higher level difficulty and the AI Director from Left4Dead! Although I think the community would love some additional official maps, I would speculate that the release of this for free has done wonders for Valve's reputation after the damage that the release of L4D2 may have done.
So here's a video to watch:
You'll need to register with steam if you've not already, otherwise like I said this is completely 100% free. The official steam page for Alien Swarm is here!