I'd want RE6 to be a continuation of RE5, but with several improvements.
1) Add much more horror.
2) Add a customisation mode for weapons and outfits.
3) No stages that take place during the daytime (screwed the feeling of RE5 completely).
4) Some actual story about the badguys so you feel some hate towards them once you finally fight them (couldn't have cared less about Irving and Excella in RE5)
5) Make the controls more fluent; right now it feels as if the controls for RE4 and RE5 was too rigid, even though it was a huge improvement from the previous games. And add a melee attack like a punch-combo or some cool-ass kicks, not just swiping with the knife; most of these characters have military/police training so they should definately know how to fight unarmed. This would be especially useful in the Mercenaries Mode (which is the only mode I play now since finishing the story mode in RE5; SS ranking in most stages with Wesker)
6) For the Mercenaries Mode, I'd want to be able to choose more characters and also be able to choose my weapons and outfit before going on a mission. If you have a total of nine slots (like in RE5) then you can choose to fill up six of those slots with whatever you have available (weapons are unlocked for MM by finding or buying them in Story Mode and then you could also transfer your customised character with his/her weapons to MM) and then also have an option to change the difficulty level from easy, normal and hard.
7) I'd like RE6 to be the last game in the series, story-wise. Bring in all the good characters, like Leon, Chris, Claire, Jill and a few other side characters like Sheva and that black guy that hepled you out in RE5, and have several storylines for the characters. Example: There is an overall story, but to play through it you have to choose one main character (Leon, Chris or Sheva) and they all have a buddy going along (which can be played by Player two; Leon has Claire, Chris has Jill and Sheva has the black guy) and then you play their part of the main story. The other characters story sometimes spill into your story, path crossing etc. And you won't understand the full story until you've played through all three stories.
And that's basically what would make RE6 the ultimate Resident Evil game for me.