Spoiler warning...
I thought Tony whacking Christopher was sad. I always liked Christopher's character. He seemed to always want to be like Tony, but had his personal demons with drugs and booze. When he finally gets his life back on track, his friends can't seem to handle him being straight. Just last week we saw Christopher grilling steaks with his new daughter and wife in the house, and Tony ragging him for not having a good time. Then in less than a week's time Chris is back to drinking and doing Coke, and Tony whacks him for failing to keep it under control. Talk about mixed messages.
It struck me as odd that Tony whacked a made guy from his own crew during the middle of an inter-family feud. Seems like you'd need as many hands as you can get.
The other thing I noted was that AJ's involvement with the College guys is an attempt at foreshadowing. Until he broke down in the psychologist's office, I was beginning to see the seeds of him taking up the family business. Now I'm not so sure.
I don't see anyone in Tony's family capable of stepping up to run things in Tony's absence, with the possible exception of Sal. Paulie would self destruct in a matter of weeks as a boss.