The series follows the adventures of hero Sam "Serious" Stone and his fight against the forces of the notorious extraterrestrial overlord Mental who seeks to destroy humanity.
The series' gameplay could be seen as a bit of a throwback to earlier first-person shooters. Released during a time where shooters were becoming increasingly realistic and more concerned with "authenticity", Serious Sam offered up traditional, Quake-style shooting. However, the more modern technology of the time allowed for a new take on that classic formula. Closed-in corridors are mostly replaced with wide-open environments, small groups of enemies are replaced by dozens attacking at any given time, and there are many hidden areas and treasures to find, often in obscure and counter-intuitive locations. Combat makes up most of the games, with Sam's only help being NETRICSA (NEuro-TRonically Implanted Combat Situation Analyser), an advanced computer AI surgically implanted in his brain.
Serious Sam features cooperative gameplay, something not commonly seen in modern PC first-person shooters. Besides network/online play, Serious Sam also allows for split screen action supporting up to 4 players and this is an even rarer multiplayer feature for PC games these days, although very common in gaming consoles.