Who are we going to be fighting? A lot of evidence points at the Forerunners themselves and definitely some Forerunner made machines. Leaks show the crawler and the watcher (1) as most may know, but the Halo CEA terminals heavily hint at more specific Forerunners like the Didact (2). There is no more flood, the covenant have been ruled out as the main antagonist for the game, so what would be left? Were crashing on the shield world/dyson sphere which was created to protect from the ring blast. Who else would be in there? Its hard to believe were not fighting the Forerunners in some way or another. There is a video which was removed from halo waypoints Forerunner terminal log in (place to unlock the last terminal) which would be shown after typing "wake up john" in the Forerunner language. link below (3). And if we just so happen to have a Precursor in the game at any time, it will be in Halo 5 or 6. So what do you guys think? Will we be fighting some completely unknown enemies which have never been mentioned before? Or will we see Prometheans Ready to kick our asses?
1- leaked enemies http://images.thisisxbox.com/2012/05/halo4toys1.jpg
2- didact everywhere http://imageshack.us/photo/my-images/841/speculation.png/sr=1
3- wake up john