Unlike Blue Shift, Half-Life: Opposing Force is an innovative expansion that adds new ideas and weapons to the world of Half-Life. The story of Opposing Force adds a great new perspective to what happened in Black Mesa and makes you go through many different areas of the facility that are completely new and exclusive to this expansion. The new enemies and weapons are also interesting and add to the experience. Even the boss fights are fun which is something the original Half-Life struggled with. Definitely give this expansion a chance if you want more Half-Life gameplay.