I think theres so much riding on Halo that makes it not as skillful as it could be, like low gravity, slow movement mechanics, rechargeable shields, auto aim, 360 degree motion trackers, and an overdose in hitscan weapons.
Not saying the game takes no skill, its just that its scale of skill is so tiny I cant stand to watch tournaments based on it. CoD and Gears are the same way for me, I cant stand watching competetive play in those.