I don't really know why Global Offensive costs less than Source, but nevertheless, this is a great game, the successor of a real legend. It's a little hard to adapt if you come from games like Battlefield or CoD because of the recoil and no sights, but if you are dedicated, you can master it in no time. If you are a fan of shooters, you MUST play this game... but warning: it'll be addicting as hell.