An excellent expansion pack from developer Gearbox! I wonder how many of us still know what expansions were... nowadays these extra stories would come in the form of DLCs not an expansion pack. It meant to indicate a longer story and this is definitely a bigger pack than a dlc which can be a single weapon or a new costume for a character in the game.
In any case, Opposing Force puts us in the shoes of a corporal, a certain Adrian Shepard, who - along with his fellow soldiers - is sent to neutralise the enemies invading the Black Mesa facility. As expected, things go awry and you are alone facing the good-old aliens. There is a new assortment of weapons, new enemies and new music. Oh, and there are fat security officers helping you!
By the way: the game comes with widescreen settings and vsync can be switched on! Just excellent!
A relatively long and challenging expansion pack that comes very cheap. It did age a lot throughout the 15 years but it is still a great game... at least for reminiscing purposes.