Many people think that it will have 4-player co-op. It will only have 2-player co-op.
It will be available November 15th for $40.00. Best Buy has it listed as $60.00 with a release date of December 1st. Eric Eckstein- "I don't have anything against Best Buy, but that's incorrect. You should expect the game at $39.99 on November 15th."
It will have at least seven Reach maps remade from Halo:CE, including one map from Halo 2.
Blog found here: http://www.g4tv.com/comiccon-2011/panels-and-live-blogs/halo-panel/119/