Here's the thing with Craig: everyone goes on about what a great actor he is, but his approach is "less is more." He doesn't go into hysterics, he doesn't break down, he's not at all "big" with the performances. It's all very low key: Bond kills with a stoic face, mourns with a stoic face, bleeds with a stoic face.
Yes, there's that neat moment in CR when he looks at himself in the mirror, covered with blood after the fight in the stairwell, and we sense (maybe) he's thinking, "What have I become?" Yes, there's the "b*tch is dead" line from the book, but again it's a case of "less is more." We know what he's feeling, but not because he shows it, rather because he works hard not to. There's the moment on the shooting range in SF where it seems like even HE is thinking, "Am I washed up?" but again, subtle: it's all in the eyes, and the way his face goes slack. If it wasn't on a big screen, you might not even see it. Craig's approach asks us to participate, to fill in the blanks. We have to meet him half way and interpret the deeper currents running under that deceptively placid surface. Ironically this is much the same approach taken by...wait for it...Roger Moore. Except with a scowl instead of a smirk.
So the challenge becomes "how much can we pile on?" How awful can we make things for Bond to get that one, fleeting expression from Daniel? If you play it for straight-up adventure, his face will stay cast in granite, but if you kill all his friends, or dig up his parents and leave them on his couch, maybe then we'll glimpse something. This is similar to the "Dalton issue." Once they'd seen how well he handled anger in TLD, they thought, "How can we engineer a movie where he's angry the whole time?" It would not have been a sustainable model in the long run.
I think the most emotional I ever saw Craig's Bond was when Silva blew up the Aston Martin and Bond gets this look of "Oh, HELL No!" Which struck me as hilarious: I laughed out loud and I wasn't the only one. I do not think that's what Mendes was going for. But when you play it as close to the vest as Craig does, any expression that's at all "bigger" risks becoming funny.
Anyway, I think if they keep Craig on, they'll have to continue with the sturm und drang just to support his style. So I'm okay with him moving on.