Made by Gearbox Software and originally released in 2001 as an add-on to Half-Life, Blue Shift is a return to the Black Mesa Research Facility in which you play as Barney Calhoun, the security guard sidekick who helped Gordon out of so many sticky situations.
Great expansion but kind of underwhelming compared to Opposing force less weapons and a shorter campaign. and this was released after opposing force. still a great game though.