Easily the best 4 player Co-op shooters I've ever played (and one of the few out there really).
It features great map designs, enemies, weapons and makes you rely on teamwork like never before.
On top of that, it's free.
I've had a blast playing this game with 3 other friends and I wish there were more games like this.
However the main campaign, despite being awesome, is very short. And after you've completed it once, there isn't much else to do that re-doing it on a harder difficulty. There are some people out there who have made a couple of custom maps long ago, but the community in general died out. The lack of Workshop doesn't help either. All we can hope for now is that Valve revives the game with new campaigns or makes a sequel.

In short: One of the best Co-op games out there and it's free. Definatly worth gathering some friends and giving it a try.

Easily the best 4 player Co-op shooters I've ever played (and one of the few out there really). It features great map designs, enemies, weapons and makes you rely on teamwork like never before. On top of that, it's free. I've had a blast playing this game with 3 other friends and I wish there were more games like this. However the main campaign, despite being awesome, is very short. And after you've completed it once, there isn't much else to do that re-doing it on a harder difficulty. There are some people out there who have made a couple of custom maps long ago, but the community in general died out. The lack of Workshop doesn't help either. All we can hope for now is that Valve revives the game with new campaigns or makes a sequel. In short: One of the best Co-op games out there and it's free. Definatly worth gathering some friends and giving it a try.