Half Life 1 is my favorite game, I was hooked from the minute I saw the the movie style credits while taking the tram ride into the Black Mesa facility. The game play itself and the enviorment it took place in is what made the game in the end. Listening to guards as they conversed, getting in three way fire-fights between troops and aliens, the crowbar
and ofcourse CRATES! Finally a computer game that made you laugh at your friends with consoles.
The story itself was certainly nothing ground breaking; just a re-mix of Doom and Aliens, with a shake of the X-Files. The end too was a bit weak. Xen was kinda cool in it's tripy style, but it was mainly a disappointing "jumping" game like Mario Brothers or Tomb Raider. The main boss was that stupid giant baby creature, bleh.... then the G-man bit.
Like several posters in this thread, it's all about the game play. Really, what was Pac Man's story? Let's face it, Pac Man didn't even have a crowbar or frag grenades.