It's the most expensive games Microsoft has ever made.
It made by a brand new studio where each member has been hand-picked from the best studios this industry has to offer. (Bungie, Naughty Dog, Retro, Gearbox, FASA Studios, Valve, Bioware, Bethesda, Rockstar, Black Isle Studios, id Software, Treyarch, ION Storm, Pandemic, Guerilla Games, RARE, Sony Santa Monica, Lucasfilms, Square Enix, Ubisoft)
Over 300+ people are involved in it's development.
The game went through an extensive pre-production.
It's gone through an extensive 100,000+ people playtesting.
It's the first numbered sequel in 5 years.
Four novels (with 2 more coming) have been written to set up this game.
A full live action series has been created to hype up interest in the fiction.
A brand new soundtrack has been created by Neil Davidge from Massive Attack.
The graphics are of the highest caliber on the console.
The characters have all been fully motion capture including their faces.
It has in-house created CGI cutscenes for the first time in any Halo game (aside from Halo Wars).
The game is launching in November (first big Halo game launching in that month since Halo 2), the biggest month for sales potential.
I'm calling it now. This game will be the biggest launch on single console ever released.