Half-Life: Decay follows a story running parallel to that of Half-Life, Opposing Force and Blue Shift, featuring two of Gordon Freeman's colleagues unseen in other games. Designed for co-op play, the player must switch back and forth between the two characters if playing alone.

How long is Half-Life: Decay?
When focusing on the main objectives, Half-Life: Decay is about 3½ Hours in length. If you're a gamer that strives to see all aspects of the game, you are likely to spend around 5 Hours to obtain 100% completion.

Half-Life: Decay will take you approximately 3 Days to complete if you play for 1.5 hours a day while focusing on some extra content.