Halo
"Wake me. When you need me." - John 117
Halo is "The" video game for me, and ever since first stepping out that escape pod onto an alien ring world, the series has held a special place in my heart.
Halo: Combat Evolved was the first time I realised a video game can be more than "number go up". They could be experiences, stories. The fun of playing your way was the point, not being 1st. Obviously that element of games in general was present, but it wasn't the sole focus. It was truly amazing.
The sequels just seemed to expand on themselves and provide a better and better experience. When I finally managed to get an xbox live subscription, the sky was the limit. Matchmaking, Custom Games, Theatre Mode, File Browsing and an ever changing hand picked selection of community made screenshots, maps and game modes. It didn't really feel like just a video game. It was a social hub, a place you could "go".
I love every game in the series (even Halo 5). I will always love every and any Halo game.