Unless you play the campaign co-op with 4 people, it really sucks. In all the firefights you're constantly playing babysitter to a bunch of spartans with no self preservation instinct. It's like a crappy mashup of Halo 4 and Republic Commando, with none of the good features of either, and all the annoyances of both.
Forge is cool tho, too bad no one plays this game to do custom games with.