...go read lore and come back when ur more versed in the halo universe. Besides the game would feel extremly awkward if MC and Cortana just waltzed through the games haveing nothing big happen to cortana...Shes like chiefs sister...Hes gonna come back pissed next game lol.
Also to the OP this game is technicaly a new beginning for Halo first was Halo CE then 2 and 3, wich was the flood and covey...Now there introduceing a whole new aspect into the game, and like someone said earlier more will be explained. Perssonaly i liked the campaign ( was short imo ) but it was somewhat challenging on normal difficulty and the story was good. I think 343 did an excellent job. But you gotta face facts 343 is not bungie so, no halo will not be the same but they can definatly try and make it better, and i think the foundation is definatly set for a new beginning in the Halo series.