Dude, they used less then a year on ODST. They only made ODST so that they could get enough money to become independent from Microsoft meaning that they could make games like they did with Halo 1. Halo: Reach is likely to be one of the best in the Halo series with good parts from both Halo 1 and Halo 3.
My estimate:
Good games & books:
Halo 1
Halo 2
Halo 3
Halo: Reach
-
First Strike
Fall of Reach
Ghosts of Onyx
Decent games & books:
Halo 3: ODST
-
Contact harvest
The flood
Bad games & shitpiss:
Everything not made by Bungie:
Waypoint piss.
Halo Whores.
Legends piss.