For people who enjoy competition, they would agree Halo 2 and Halo 3 multiplayer was on point with the ranking system. Being a naturally competitive player myself I was a die hard Halo fan since day one. I love competitive leveling systems such as the ones implemented in both Halo 2 and Halo 3. Unfortunately that all changed when Halo Reach came. I quit playing Halo because it became boring to me. Even though there were ranks that people got with the build up of experience, I had very little interest because it did not matter if someone was good or bad to get high rankings. Then when Halo 4 came out with a new company (343 Industries) I had high hopes they knew what the Halo community loves because they were fans themselves but it turns out they did not. Their ranking system mocked Call of Duty in my eyes, you played games to get experience and then you would unlock armor when you hit certain ranks while in Call of Duty you would unlock guns. This caused me to quit Halo 4 as well.
After Halo 3 the next two games failed, Halo Reach and Halo 4. I mean no offense by this but the Halo community was at its all time largest during Halo 2 and Halo 3. After Halo 3, many players quit shortly after playing Reach. Then 343 made some improvements launching Halo 4 but it was not enough to restore the Halo community back to it finest. When you look at the big picture, you will realize that the competitive multiplayer for online play is what builds the foundation of the Halo community.