I found Half-life to be an immersive game with an excellent storyline. The graphics were state of the art for when the game was released but feel dated compared to some of the newer games. Half-life has definitely raised the bar of FPS from where they started with Doom and Castle Wolfenstein 3D to a game you have to think in order to beat. There's more to this game than just running around laying waste to "baddies". The AI is a refreshing addition to a ground breaking game.
Overall I recommend Half-life to anyone who's both a Sci-Fi fan and a FPS fan.