Winter!: Prepare for holiday gaming!
The areas you see in the intro on the train show areas you play through which was interesting gameplay concept as players advanced and although they didn't know what was ahead, they'd have ideas on what an area was they were in from memory. The half-life series was also a popular FPS title and if the amazing storyline wasn't good enough for you then the expansions and the modding community was. I remember playing on mods such as: Science and Industry, Sven Coop, Natural Selection, Bumper Cars, They Hunger, USS Darkstar, CounterStrike1.3 .. the list could keep going on and that alone has to have me rate this game as 5/5.
Game Traits applied to Half-Life (PC) by DarkOnistar