The levels in the PS2 version of Half Life aren t extended per se but in certain areas they have been improved significantly over the PC version That means in some cases there s an extra room here and there Before the Hazard Course you actually get to walk around room that the elevator brings you from there s a small added transition room added when you re swimming through a pipe in the Lambda Core chapter etc I don t know if these would qualify as extended but the PS2 version of the HL levels do contain improvements and small additions