You know, you were right, I was rather insulting in my post, and I apologize for that. I unfortunately see far too many troll threads to keep the ol' "counterattack" instinct under control all the time. However, you should realize that your tone does not help this instinct; I'm reading less "seriously, what am I missing here?" and more "hurr old game sux" from your original post.
Half-Life 1 was best known for presenting both its gameplay and its narrative in a wholly unbroken continuous format. There were no cutscenes, no "meanwhile" cut-aways, and very few drastic map changes; rather than individual, self-contained "levels", you could run around in entire sections of Black Mesa, and see what your actions on one map accomplished on another. While this wasn't unheard of, Half-Life 1 pulled it off with panache, and that's what made gamers sit up and take notice. It may seem rather commonplace by now, but this paved road was once a trail that HL1 helped blaze.
I'll admit that the actual story in the game isn't anything spectacular (scientific experiment goes wrong, aliens invade, soldiers come to "clean up"). But the fact that, aside from one brief episode of unconsciousness, you experience the whole thing as a very long day in the life of one extraordinarily unfortunate theoretical physicist, and that half the story is waiting to be found in nooks and crannies- there are still games today that struggle to show that sort of experience.