What aspects of all the Halo games do you want? from H1, 2 and 3.
For me this is what I want:
H1:
Plasma rifle stun
Plasma pistol (doesn't to need to lock on but make the rapid fire more powerful than in H3)
Strong Grenades (ability to carry 3 or 4)
Stronger Rockets
Halo 1 version of the AR
Scorpion tank where friends can ride on the front
H2:
Rocket lock on for vehicles, if not for warthogs and mongoose atleast for wraiths or something cheap
Sniper Rifle with Night Vision
Battle Rifle from Halo 2
H3:
Maybe the bubble shield, lazer would probably work for Reach.
Hornet