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Serious Sam: The Second Encounter is an FPS from Croteam and Gathering of Developers. You play as Sam "Serious" Stone, and do battle with thousands of alien nasties throughout various historical set-pieces, using an array of diverse and enormous weapons.

Close Combat: First to Fight is a squad-based military first-person shooter. The player commands a fireteam of 3 other U.S. Marines in a realistic, though fictional scenario where the United Nations sends Marines into Lebanon when their Prime Minister falls ill and Syria and Iran send forces to bolster certain factions.

Civilization III is a turn based strategy game from Firaxis Games and Infogrames. The basis of Civ 3, like in the previous two, is building a civilization from a primitive tribe to a modern empire, developing cities, technology, and culture, and conquering weaker empires while making peace with stronger ones.

Full Spectrum Warrior: Ten Hammers is the sequel to the Full Spectrum Warrior.

Command & Conquer: Red Alert 2 is an RTS from Westwood Studios and EA. In the alternate universe where Germany never rose to power, the Allies and Soviets are at it again, but this time the Soviets have launched a full scale invasion of the US. You can command Allied forces and repel the invasion, or command Soviet forces and lay waste to the US and its allies.

Quake 3 is an online FPS from Id Software and Activision. In a departure from its predecessors, it completely lacks a traditional singleplayer campaign, and the emphasis is mostly on deathmatch.

Half-Life 2 is an FPS from Valve Software, and was one of the most highly anticipated sequels of all time. You return as Gordon Freeman, the strong and silent-type physicist, and you must do battle with an alien race of enslavers to liberate the surviving remainder of humanity on earth.
Also applies to Half-Life 2 Lost Coast free downloadable level.

Deus Ex is an FPS/RPG hybrid from Ion Storm and Eidos Interactive. It is most notable for its free-form skill-based gameplay, which allows nearly unlimited solutions to missions, often allows for multiple outcomes, and lets you shape your character to be best suited for your style of play by allowing you to develop the skills of your choice.

The Chronicles of Riddick: Escape from Butcher Bay is an FPS from Starbreeze Studios and Vivendi Universal. The plot serves as a prequel to the 2000 film Pitch Black, and features Vin Diesel's voice and likeness.

Call of Duty is a WW2 themed FPS from Infinity Ward and Activision. The game is played over three campaigns; American, British, and Russian, and most of the missions emphasize fighting as a company over lone wolf tactics.