I've been having this problem for well over an hour now.
It's really aggravating me. I can't play games properly. It's not letting me use my custom classes, not showing my Spartan the way I have customized him. Not giving me proper XP rewards for winning (or simply just playing) on matchmaking games. It kicked me out of my "Roster" party that I was playing with and now will no longer let me join into my friends games or let my friends join into my games. However, my friends are not experiencing any of these difficulties (at least not yet, hopefully I didn't jinx them!). I played through the campaign co-op with 3 of my friends. It was great except fairly laggy for me, since, I was host. Hopefully that can be resolved soon.
I really want to play online now, Spartan Ops and matchmaking, but it's not allowing me because it is saying, "The Halo 4 servers are not available. Please try again later. Matchmaking has switched to using the default playlist." and then just changing to a screen that says "The Halo 4 server is not available at this time. Please try again later."
It's really bothering me. And I highly doubt, although it would be extremely nice, if the players who are being highly affected by this, to the point of not being able to actually play the game, could get some free things. At the very least, the XP that has been taken away from us during this time.
Hopefully you're already looking into the problem, 343, but if you're not, hopefully you're hearing your fan base in agony. Please help soon.