: I haven't played that many first person shooters. Is there any that truly
: delve into the protagonist's personality?

It did a very good job of fleshing out a character who is weary of war, and just barely holds out hope for something better. It also did what 343i tried to do even better, because the protagonist was the most generic player-vehicle of generic player-vehicles in the previous games. He never spoke in Wolfenstein3D or in Return to Castle Wolfenstein, and in the latter game he only appeared in the beginning and ending cutscenes.

Of course, it did this partially through the use of internal monologues. We hear BJ Blaskowicz lamenting that war is all he knows, and the heavy brooding and exposition is broken up by some funny, and rather human, moments of humor.

"Okay...okay. So you put a Nazi on the moon. Fuck you, moon."

Are we ready to hear that from the Chief? Not just his gruff acknowledgment of orders and pithy one-liners, but what he actually thinks of the world? The random thoughts that pop into his head when he sees a pile of dead bodies or a formidable new enemy? It could be done in a game where he was truly alone (though a fat fraction of the fanbase would inevitably declare Halo to be Ruined Forever) but in a game with the rest of Blue Team, they really need to talk to each other. The dialog has to be concise, professional, and meaningful. I don't think the current crop of 343i writers could deliver that.

: maybe they can explore themes or
: have great plots but, I think, the first person shooter's mechanics are
: not conducive to the exploration of a character's internal mental state.

Wolfenstein: The New Order also had downtime levels where you weren't shooting anything, just walking around and talking to people. It worked rather well.

: To me, that is book territory. Or films, or plays.

: And you have the double story telling burden of the friendly NPC AI. How to
: you have pathos or gravity when the Chief is hanging out with the Keystone
: cops? How can you mistake them for awesome Spartan super soldiers?

Design them as awesome Spartan supersoldiers.

I've been thinking about this with regards to Reach, and I think I know how to do it. At least, I know how to do it for Jun. He should have stayed off the map in Nightfall, sniping enemies from afar. When you see three Grunts dropped by three shots in less than a second, you know that you are backed up by a supersoldier. To solidify Jun's presence, he could occasionally pop in to assassinate a distant enemy, somewhere that you can see but far enough away that he won't be kill-stealing.

In the meantime, make Noble 6 more important. Implement more enemies located where only she can deal with them, and give her more objectives to accomplish.