Bungie announces....Halo 3?? Err. Hmm..

Since Microsoft pulled the plug on Bungie's announcement at E3 this year, fans of the company have eagerly waited for news on what the company is up to. Today Bungie released the first teaser trailer for their next project, one year after Halo 3's debut on the Xbox 360. 

Titled "Keep it Clean", the trailer depicts a futuristic city presumably being attacked by an alien invasion force, but is it? Perhaps it's something else? A screen during the trailer mentions a "metropolitan disaster", a Halo 3 logo eventually appears, but what does it all mean?Have a look at the trailer and debate in the comments!