It may not be game breaking, but it sure as hell is mood breaking to not have an option to toggle mid-game joining in matchmaking.

What is, however, game breaking is this game's rediculously low object garbage collection threshold. May Bungie have mercy on your soul should you die in MP/Spartan Ops and have one of the few power weapons, cause that shit will be zapped from existance. Or temp swap your power weapon for another weapon to thrash the AI, cause it will be collected once you go back for it once a checkpoint or zone load is hit.

Also, the UI is horrible.

And where the fuck did campaign matchmaking go?

And the gravity hammer was there in the last mission. There's an achivement for it.