There was a time when first person shooters were simple. You played the infallible hero, and almost everything in your world was against you. This simple setup carried you from beginning to end, with an increasingly devastating arsenal leading to an exponentially rising body count. Level layouts were complex, hiding many divergent paths that often led to dead ends, where hidden goodies were stashed for the most thorough of players to benefit from. Treasures ranged from keys necessary for progression, ammo or health which was always in short supply if sticking to the main path, or often treasure itself adding to a post-level score. Everything was in the name of fast paced fun, and no one dared to mess with the winning formula.
Then Half Life was released.