Andy Murray needs to improve his second serve which is stating the obvious, however it has always been an evident problem however never been all that costly, whereas over the last two tournaments it has, Fish was really hurting Murray off the second serve returns as was Soderling therefore allowing them to both break Murray many times.
At the moment his mental approach is also a problem along with his forehand, however the two kind of go hand in hand, for example when playing Nadal regardless of the head to head Murray knows all out aggression is the only thing that will get it done, therefore his mental approach is sorted in regards to aggression therefore enabling him to hit aggressive powerful forehands, however if he is in two minds in regards to how to approach a match or an opponent you can see he does not want to really go for his shots therefore making his forehand a very vulnerable shot and in many instances just sitting in the middle of the court for his opponents to punish.
His volleys are very solid however still over rated based on the fact that if you listen to pundits and commentators you would think he volleys like a doubles specialist which he certainly does not, his smashes are also good but sometimes like his forehand a little bit too conservative.
His backhand, 1st serve, conditioning, returns and defence are awesome and therefore I would consider these the only areas of improvement that are really holding him back at current. Mainly his mental approach though I must say.
the first thing which strikes to mind about murray is his lifeless forehand........
agreed with the rest of your list as well.......he has different approaches for different opponents but sometimes he is caught in dilemma and ends up getting overtly defensive both gamewise and mentally.......