I don't have strong feelings about the Halo franchise one way or another, but seeing the Halo 4 teaser sent up my cynicism flag. I can't help but hear "cash in!" ringing in my ears.
Not to say that I KNOW it will be bad game, but Bungie is gone. Sometimes an IP can find a new identity under new development lead, but usually when the original creator of something leaves, the "magic" goes with it.
And I know that the following is really cynical of me to say, but it's true...
Despite being rushed by their Microsoft overlords to meet release dates, I truly believe that Bungie made Halo as a labor of love.
I don't know if the 343 studios people are committed to doing something good with the IP, but I do know that Microsoft is making Halo 4 to make tons of money, period. Microsoft would likely execute Master Chief in a public square if they knew it would make billions.
...
I guess I went on a tangent there...
Anyway, I'll give a flip about Halo 4 when they tell me that the Arbiter is in it, the Arbiter is playable, and he gets to share the stage with the Chief, just like he did in Halo 2.