While I think adding story to multiplayer is unnecessary, and certainly shouldn't be a selling point, I don't necessarily see it as a turn-off. It's inconsequential. Multiplayer may be stale to you, but I think that has to do with Bungie trying too hard on new features (dual wielding, equipment/armor abilities, loadouts, reticle bloom) and not spending enough time on the more important aspects of a multiplayer game like weapon balance and map design. Is 343 going to do the same thing? Maybe. I don't like that the battle rifle is back. The DMR (or a similar weapon) would have been perfect.
As far as campaign goes, I don't really feel like it's been necessary to present the Master Chief's backstory in a game yet. The dynamic of a faceless hero against an entire army with more advanced weaponry was great. Like they said, his story is available to those that want it in the books (particularly "The Fall of Reach" and "First Strike"), but it wasn't vital to the games. Now that the Covenant is (presumably) defeated, though, they have to go somewhere. I guess I'll reserve judgment until I hear more about it or actually play it, but three of the four campaigns have been very good. I hope this one lives up to them.