Half-Life - Scientist Slaughterhouse (Steam Patched)

The story, if anyone is interested, puts Gordon Freeman (the player) as an agent of an advanced weapons corporation called Death & Destruction Inc. (DDI). DDI on the other hand takes orders from an alien military force known as the Nephilim Alliance (NA), originating from an alternate dimension. The problem is loads of scientists are appearing out of nowhere and they need someone to get rid of them...