(EDIT) - Seriously? No, his ass will not be the new enemy. The new enemy is the 'Prometheans', they are Forerunner defense AI's. Expect a challenge, the Promethean knights look like a huge threat!!
Knights - Main infantry.
Crawlers - Fast, agile, but weak infantry.
Watchers - Guard Knights (Increase shield strength, catch grenades etc.)
(EDIT) - Awwww =( I wanted to fight that guy's ass
The Main Antagonist is supposedly the Didact, but of course there is no confrimation yet.