Sam "Serious" Stone is a warrior from the future that is sent back in time to stop Mental and save the future.
Many see him as a parody of Duke Nukem and the game a parody of other first person shooters.
Serious Sam is also notable for it's humor and parodies. All the game has you do is shoot enemies and get to the end of the level but it does the few things it does well which has allowed it to receive top editor awards. However it's simplicity is where the meat of the series resides. The game itself has been often described as an arcade first-person shooter much like the older Doom or Quake franchises. The second encounter was released in 2002 which was a time when many complex and deep first person shooters on the PC had been released like Deus Ex, System Shock 2, and Half-Life. The series is known for it's insane amount of enemies and it's gigantic bosses. He runs (constantly) fighting against a very large number or various alien enemies. The game is broken up into three different sections in this game as opposed to one main location in Egypt in the First Encounter. The game features Sam "Serious" Stone on another adventure through more varied environments than the first. This is not an expansion but the second part of a larger two part game in which the second encounter builds upon the first. Serious Sam: The Second Encounter is the more robust continuation of the original Serious Sam: The First Encounter.