

While new creatures were added, there were no additions to the game's current weapon arsenal. Other new additions include the Zombine, Combine pods and Hunters the latter two introduced as set-up for Episode Two are only briefly interacted with. Enemies such as Stalkers and areas of the Citadel glimpsed at the end of HL2 are encountered and explored by the player. Like HL2, the gravity gun continues to play a crucial function throughout the game, granting the player extensive use of physics in combat and puzzle-solving. Episode One also integrates tutorial like tasks into the story itself as in the previous games in order to familiarize the player to any new gameplay mechanics, such as the ability to re-program rollermines, without breaking immersion. The gameplay is broken up between combat orientated challenges and puzzles these include physics-based puzzles. As in HL and HL2 players make their way through a linear series of levels, encountering various different enemies and allies. As a direct continuation of HL2, no significant changes to the gameplay were undertaken. Alyx and Gordon re-enter the Citadel to try to stabilize the core. Eli reluctantly agrees when he sees no other option. Kleiner states that the explosion could be large enough to level the whole of City 17, and that the only way for them to survive would be to re-enter the Citadel and slow the core's progression toward meltdown. Alyx contacts Eli Vance and Isaac Kleiner, who have managed to escape the city, and is informed that the Citadel's core is at risk of exploding at any moment. Dog removes these rocks, and Gordon is reunited with Alyx. Gordon wakes up outside the Citadel, buried under a pile of rubble. More Vortigaunts then surround and teleport Gordon. As he opens his mouth to speak, he is distracted by blue lights and is separated from Gordon by another group of Vortigaunts - much to his displeasure. The G-Man is then seen walking toward Gordon Freeman. As time stops, several Vortigaunts appear and rescue Alyx from the blast. The series of following events in HL2, Episode One starts out after the explosion of the Citadel's dark fusion reactor from which Gordon was extracted by the G-Man and Alyx Vance was left behind. Episode One continues to follow scientist Gordon Freeman and his companion Alyx Vance as they deal with the events of HL2 and humanity's continuing struggle against the Combine. The episode takes place immediately after the end of Half-Life 2, in and around the war-torn setting of City 17. Settings: City 17 and its outskirts, somewhere in Eastern Europe (Bulgaria, Romania or Ukraine).
