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

In Bioshock Infinite, the protagonist's personality (personalities?) is a huge part of the plot, and it works well, because much of that is explored through the impact that his actions and choices have on other people, and not through sappy conversations that he has with those people (show don't tell?).
Minerva's Den is another game that did it well, but that was also due to a narrative twist, where the player didn't know that the person being explored throughout was actually himself.

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

From a narrative sense, I can think of quite a few games that do it REALLY well in a way that works better as a game than as a film (The Last of Us is probably the most obvious example, but stuff like Logan has shown that a similar premise also works well as a film in its own way).

: 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?

Not sure what you're saying here... I'm sure there's an inside joke that I'm missing, so I don't want to make opinions when I'm not quite in the loop...