The Halo series is one of the best series franchise that was ever created, and it is one of the most hyped title. The series started with Halo: Combat Evolved and the latest is Halo Reach, no wonder why this series has this much of popularity, it all started from the very first killer app. The series has an overall natural feeling of epicness for the fans, the answer to the question is the fan. Without the existence of the loyal Halo fan, it wouldn't be that popular.
The game has a story that grabs the reader or the viewer more into it, and gives him lots of questions and answers as well, it is very interesting and complicated. The range at which the story takes place is huge and epic, starting with the ancient Forerunners wars with the Floods and through Human Civil conflicts to Covenant war and Flood domination into peace. This huge plot with tiny little stories, tons of it in each phase, the saga of the elites and the Arbiter. The origins of john-117, and the saga of the Halos. It is just incredible how the fictional universe of Halo was created and developed, it is just so true we can feel it as an alternative dimension. The amount of characters and each's origin and role in the universe, the large amount of technologies and information about everything makes it a huge series.
The Master Chief, John-117, probably the main reason of Halo's popularity. The character of the chief is so plain and simple, with no expression at all since his face is covered the whole time, but though the chief's character is far more complex and complicated by the fans. The fact that his face was never shown, and the assumption of his face being the helmet's glass sometimes, it is the mystery behind that green helmet. Master chief is one of the most popular character within a game's fan, you can tell he is higher in popularity and hype than Chuck Norris in the internet culture. Yes, indeed, it is the internet which also helped to rise this game's popularity.
When the release date for Halo 3 was announced, tons of advertisement were thrown all over the world. You can tell that each person on earth knew about Halo or the Master Chief, he was everywhere. On the streets, on subways, over the internet, TV and even soft drinks. It has stick itself to the culture, this Halo series. And with the end of the series, Reach being the last, the life of this series is still unkown. But predictions were made, and it was guaranteed that the Halo era would last for another 30 years.