portal game series, two main games, Portal, Portal 2, first-person puzzle-platform, female protagonist, Chell, Aperture Science facility, GLaDOS, artificial intelligence, companion cube, portal gun, physics-based puzzles, clean white laboratory, advanced technology, dark humor, atmospheric lighting, immersive gameplay, science fiction environment, 3D environment, detailed textures, interactive objects, strategic thinking, problem-solving, single-player campaign, multiplayer co-op mode, Portal 2, dynamic lighting, high-resolution textures, complex structures, engaging storyline, Valve Corporation, Source engine, critically acclaimed.