Do you remember when the Halo campaign had a more gung-ho feeling to it? We haven’t had that feeling since Halo 3, and that is because the gung-ho personality was within Avery Johnson. His humorous quotes were perfect to add to a “shootem up” feel. The game lost this, which is why we saw Halo start to take itself a little too seriously.
I think having a major character that is the face for marines was necessary, as marines were a big part of previous Halo’s campaign missions. In my opinion, I enjoyed fighting alongside marines much more than other spartans. You don’t feel like a super soldier when every ally is the same. Then you just feel like a futuristic soldier. We haven’t had that many marine interactions since Halo 3, and i think its because they lost their head character and feel insignificant now. This is why Halo feels so different, and ultimately not as enjoyable (for me)