Half-Life 2 is baisically what got me into serious gaming.
I had an xbox (original btw) sure, but all I really did was play the occasional Halo 2 on it. But on day my friend was over at my house (he was a big gamer) and he brought his 360 so we could system link and each have our own screen and stuff. He had this old OXM demo disc in his 360 for some reason (they dont even work on 360 :lol ) but he just kinda set it on the floor, and then put in Halo 2.
So after he went home, I found that he left the demo disc on the floor.
So I popped it into my Xbox 1 and started playing all of the demos just so I could play something diffrent besides Halo and NCAA.
So I eventually got to the Half-Life 2 demo. I had never heard of the game, and even thought it looked stupied from the preview image (it showed a picture of Ravenholm with all these headcrab zombies everywhere). But I played it anyway (it was the Ravenholm level, pretty much in its entiertey [sp?]) and I was blown away by how awesome this game was.
The game was just so much more realistic than anything I had ever played at the time - the physics, the destruction, and the "no-cutscene" presentation.
I baisically just repeated and eventually mastered the demo over the next 3 days. But then I got tired of the demo. And about a week after that I was at Circut City and saw the game on the Original Xbox for like $5 or something dirt cheap like that, so I got it.
When I finally finished the game my mind was blown to pieces. The characters, the presentation, everything felt so real and immersive.
After playing the game was when I became particular about story in a game. Before then I just cared about having multiplayer.
I eventually picked up KOTOR after that, a game which I had heard had an excellent story, without even having the slightest clue what an RPG was.
So then KOTOR threw me into the world of RPGs, which is what I mainly play today.
So Half-Life 2 (and KOTOR) are responsible for my love of gaming
EDIT: holy shit that was a long post.......