Half-Life: Opposing Force is the expansion pack for Half Life, But not by the creators of the orginal game Valve but by another company called Gearbox. To install this game you must have the orginal game half life installed on your system. You don't play Gorden Freeman here, You play Adrian Shephard a 22 year old marine sent to the black mesa to deal with the aliens and Gordon Freeman, He and his men crash into the black mesa and they are rescued by the scientists, Now he must fight his way out of the black mesa with the help of other marines, But unfortunatly the aliens are not the only ones he needs to deal with, The goverment has sent black dressed assasins to kill all the marine's, He needs to deal with them too, You could see gorden freeman too. The Level design is good but nothing compared to the superlative half-life level design which has an infinte replay value. While half-life started and ended on a tram, Opposing Force starts and ends on a helicopter with the same ending.