And from what ive heard their just going to use reach's MM (AAs and DMR's) and give us halo 1 maps, half of which will most likely be Forge World (jk)
And now there seems to be a big rift in the Halo Community. A lot of players (mostly noobs who sucked at halo 3 and 2) are saying reach is>Halo 3m and that they sould keep everything the same. while all the good players want Halo 4 to be identical to halo 3. No matter what 343 does i feel a lot of people will not buy Halo 4.
I think 343 will do right by Halo... If they are following in the footsteps of Bungie then you can almost be sure that some people will absolutely love it, and others will attempt to hate it to death (in terms of multiplayer).
As for Anniversary it was already confirmed that it would not have it's own multiplayer, but DLC classics for Halo Reach.