Halo Waypoint has released a new 10-minute video documenting the Prometheans, Master Chief's menacing opponents in Halo 4.
These towering tough guys have three sub-classes and work together in dynamic ways. The Knights are 12-foot-tall, sword-wielding hunchbacks with flaming skulls, while the Watchers are a flying support class that can throw down shields on Knights and regenerate them. The Crawlers appear to be more reptilian-like enemies who can scale the environment and rush unsuspecting Spartans who've had their shields knocked out.
The developer diary above discusses iterating the Prometheans and gives us a look at some early concept drawings. It also goes into 343's design philosophy when coming up with the new Forerunner architecture and the weapons Chief will stumble upon in Halo 4.