Bungie has wanted to tell the Halo story from a new angle for a while. Apparently, it had grown tired of telling and re-telling the story of a lone space marine cliché in the middle of a clichéd fight with invading space aliens. It's first attempt at breaking out was 2009's Halo 3: ODST, a game that didn't even feature the Master Chief.
It tried again with 2010's Halo: Reach. This time the story revolves around a squad of similarly-skilled marines. This should have been the perfect venue for Bungie to stretch its legs, but anyone who played it probably noticed that Reach also fell victim to the cliché bug as demonstrated by this Machinima video.