Eh. I don't give one about multiplayer, as I have found that there are other games that have much more replayablility. However, I get a bit annoyed when I hear the Halo 3 Brigade coming and saying how new players ruin the series, and saying how we should essentially have a Halo 3 clone. Bonus points if they try bringing up K/D, 'casual', or other derogatory terms for players who prefer other games. And of course, the classic 'return to CoD'.
Me? I think the campaign is what is integral to Halo. The camapign was what attracted a multitude of players all those years ago- before Xbox LIVE even existed- and it's the only thing I care that much about in the series.
Oh, and forge. Can't forget forge.