All 4 games come together to create a sort of grander picture of the Black Mesa incident, and I have to admit, it works extremely well for the game. Decay follows the story of two of the scientists working closely with the project. Half-Life: Decay is the most out of place game in the series, as it's the one game in the series that's co-op ONLY, though you can play with a bot should you be desperate enough. It should be noted that Blue Shift is only considered 'mostly canon', it has some small inconsistencies with the series, but is still mostly accurate. Blue Shift is the perspective of Barney, one of the security guards of Black Mesa who returns later in Half-Life 2.

Opposing force is the same game from the perspective of one of the Marines who gets separated from his team before finding out what they are actually there for. The original is obviously Gordon Freeman's perspective. To start with, there are 4 canon games involving the Black Mesa incident depicted in Half-Life: Half-Life, Half-Life: Opposing Force, Half-Life: Blue Shift, and Half-Life: Decay.

Half life ps2 vs pc