No, it's called Master Chief had his trilogy. It's time to move on.
Master Chief is kind of a dry character, but he's badass.
I've played two Halo games--the first and the second. The second had some great ideas and a number of improvements, but I hated playing as the Arbiter! It always felt satisfying to get back behind Master Chief's helmet.
I think it'd be a mistake to release a numbered sequel without the main character.
If people talk highly of the campaign I might end up picking it up after it's release when it has come down in price. At some point in my gaming past I might have cared more about multiplayer, but these days what I really look for in a game is an interesting and developed world to get lost in. So I can't really justify the $60 for this game initially unless the campaign is really well done. Perhaps I'm in the minority, but the multiplayer is a non-factor for me. I don't even have a Xbox Live Gold subscription as I'd never use it.
Yeah, I don't give a crap about multiplayer either. Halo 1 and 2 were decent but not exceptional single-player shooters. Nowhere near Goldeneye, Perfect Dark, Doom, or Bioshock (which, from what I hear, was itself inferior to System Shock 1 and 2).
I'd pay $30 for a similar experience (and I did the first two times), but not $60. I don't really know where the series has gone since then, though; maybe it's single player missions have been more fleshed out.