Very good campaign; multiplayer probably outranks Halo 2's multiplayer, but it stays in 2nd due to Halo 2's magnificent campaign.
2
Halo: Combat Evolved
Overall good campaign and multiplayer, but neither game modes out-perform Halo 2 or 3.
3
Halo: Reach
Extremely good multiplayer, great armor customization, but a lackluster campaign.
4
Halo 3: ODST
Decent campaign gameplay and story; Firefight is fun but can get old.
5
Halo 4
The campaign story is actually really good and gives lots of important insight on the forerunner-human lore. However, the gameplay for both the campaign and multiplayer is just sub-par.
6
Halo 5: Guardians
Takes Halo 4’s campaign story and shits all over it. Multiplayer is on par with Halo 4.