"Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth."
-Marcus Aurelius
Halo was a victim of it's own success. Look at all the different game modes and game types Halo has given people over the years. Co-op campaigns, forge mode, theatre mode, file sharing, Hardcore competition, relaxed social gaming, griffball, living dead, racing, zany custom games. The list goes on and on.
If you ask 10 people why they love Halo, you'll probably get 10 different answers. The problem Reach had is that there were many different sub-communities to cater for. Sometimes when you try and please everyone, you just please no one.
The best thing Halo 4 could do is go back to being a Sci-Fi shoot 'em up. The other, more novelty, gametypes would make excellent stand alone titles on XBLA. Just imagine an official Griffball game.