When I used to play Halo 3, I got so in to it, I actually enjoyed reading up on the backstory of it, like the previous types of AI bfore cortana, different planets, the 'scientific' names of the elites and brutes. I was pretty immersed back then, but now not so much.

Playing games, is a lot different from making games, trust me. In my first year of University, one of my modules was 3d game design and it wasn't much fun. But if you really want to get started, then do what RiseAgainst12 said, and study it at college or University. Just make sure that it's really what you want to do though.