Serious Sam HD: The Second Encounter is a remake of Serious Sam: The Second Encounter. The player takes the role of Sam Stone who has to kill evil aliens. The basic gameplay consists of walking through linear levels while killing masses of brainless monsters. There are three scenarios (South America, ancient Mesopotamia and medieval Europe), various weapons (three new ones in comparison to Serious Sam HD: The First Encounter) and power-ups which increase Sam's abilities.
Besides the updated graphics and 15 new secrets the single-player mode is unchanged. There are, however, a few new multiplayer-modes (team, versus, survival and co-op modes) and Steam-related additions like achievements.