1. I would like a longer campaign, but it may cause for pointless filler that doesn't contribute to the storyline. As far as I'm concerned as long as they have firefight-like mode quality over quantity when it comes to campaign.
2. As someone who reads all the books I think what they did with Halo 4 was perfect. The campaign can be understood without looking at other media, but it stills rewards you for looking through all the cannon.
3. I agree, bring back the Arbiter with a cool more hi-tech look.
4. This could be especially emphasized by killing off whatever character we bring back.
5. I don't agree. They used the flood too much in the past, but they make for a fun change of pace, a short 20 minute flood outbreak on an installation or Forerunner lab (which is then contained) could make for an exciting part of a level.
6. Give us a knife selection for customized assasinations!
Combat knife - Standard UNSC knife etc.
Energy dagger - Similar to energy swords they are standard issue for Sangheli. UNSC began to give them out as commendations when they realized their popularity.
Promethean sword - A cut down version of the Promethean sword. UNSC gives them to elite soliders due to their effectiveness in case of a flood outbreak.