Dante's fire arms should include: E+I, Shotgun, dual sub-machine guns, (long range) missile launcher, Minigun, Laser gun.
Devil arms: Flame longsword, Wind imbued gauntlets, Ice halberd, Electric katana & Yamato (dual wield), Rebellion and holy dagger.
Dante should NOT be as cocky as in DMC3 and 4. He should talk a bit but IMO Dante should be more serious than comedic.
Do not let Lucia back into the series!
In the end Dante should be challenging either Vergil (who's skills are now refined to perfection) or some huge bad-ass megalomaniacal entity who can whip up maelstroms of hugely damaging attacks (like Mundus from DMC1).
Devil trigger should not make you nearly invincible, instead it should quadruple your attack power. You should be able to properly fly (like in DMC2).
Get a new time manipulating thing.
Vergil should definitely be in it.
The area should be quite enclosed like a citadel or a castle.
There should be a fully interactive environment (smash enemies into things, pick up stuff etc)
Nero is banished from the series (sorry but, long story short, I completely abhor him).
That's what I'm hoping for.