Half-Life: Decay is the the third expansion pack for the award-winning game, Half-Life. It was included as part of the PS2 version of Half-Life. Decay returns to the setting and timeline of the original story, albeit portraying the story from the viewpoint of a different set of protagonists: two scientists working in the Black Mesa Research Facility. Decay is a cooperative multiplayer game, designed to be played by two people working together to pass through the game's levels.
Nothing much to say here, it's your usual Black Mesa styled shooter, nothing special. The story isn't great and the levels aren't very beautiful! But it's the gameplay that makes it special. Playing with another player is very fun! You can also play with a bot with the PC version but you have to control both characters, and it will be very hard and frustating! Grab it, it's free! I have included a download of Decay in the downloads section if you are interested.