The original half life is, and will probably remain, my favourite game ever. It was beyond anything I've ever played in 1999, and is still better than most modern games apart from graphics. Superb pacing, foreboding atmosphere, excellent and aggressive AI, top-notch level design (Black Mesa is still one of the best settings ever to be featured in a game), amazing set-pieces (who can forget blast pit or surface tension!). Only game that got close was, surprise surprise Half life 2 and episodes. City 17 and Eastern Europe doesn't instill the same sense of dread as Black Mesa, so that put Half-Life 2 just a notch below the original.