The campaign was a similar length to what could be expected, Halo games simply aren't that long, Halo CE was a fair bit longer because the maps were big (and sometimes largely empty) and backtracking was common, Halo 5 is slightly longer than the other recent Halo games.
My main problem with the campaign is the whole Locke vs Chief thing never went down as advertised, neither ever tried to kill the other, neither was viewed as a traitor, there was no real spartan vs spartan action.
My main problem with multiplayer is the lack of BTB and infection, and no BR starts in anything.