I just thought of another think that bothered me: stakes.
Once Silva's real goal is revealed, to kill M, the stakes go out of it for me. It seems small and easy--or should've been easy, but why kill your victim easily... but, I've talked about that. Basically, we have a two and a half hour Bond movie where the stakes are about saving the life of 1 person.
The NOC list is forgotten. Silva has no other goal. He doesn't want to take over the world. He doesn't want to make England pay. Just to kill one person. Which he succeeds in doing.
At least in Goldeneye, THAT former spy burned by the British Secret Service, wanted to make England pay AND make a shit load of money AND throw the world into the dark ages (right, can't remember) the stakes were HIGH. If Bond doesn't succeed the world is OVER.
In Skyfall, if he doesn't succeed, an old woman, who was probably going to retire soon, would be killed and then replaced...