Oh man, do people love Portal. They love the dark humour of sentient killing machine GlaDOS, the lack of conventional enemies for what looks on the surface to be a first-person shooter, and the charmingly puzzling challenges the whole portal gun puts forth. It's also nice as a counterpoint to Half-Life, Valve's other main franchise, which tends to be cloisteringly grim and humourless with its whole "aliens taking over the world and putting humanity into indentured servitude" thing.Well, Portal 2 isn't exactly free of terror, either. The game is full of creepy Easter eggs relating to Doug Rattman, the lone survivor of GlaDOS flooding the Aperture Science facility with poison gas. And went a bit nuts in the process. You can 'port yourself to hidden rooms covered in his deranged scrawls, use a radio to decode messages in others, and if you so fancy - dig further into the game's source code to discover some...disturbing audio files.