Having closely followed EV's work during 08-09 and 10-12 when he was coaching Olympiakos, one thing is certain: he is not the naive Yes man that people here present him to be. On the contrary, not only he is tactically well-versed, but he is a team builder. He is not the type of coach that will make the master-sub which will win the game (look at Italian coaches for that skill), but rather a hard worker that can build from scratch, not unlike Pep, and create an amazing team that can win by playing beautiful football.
The scenario of him having deteriorated as a coach during his spell at Bilbao IMO - without having followed him that closely the last years to be honest - is not very probable.
His coaching style is suited to top league teams that are usually dominant, and not mid-table teams like Bilbao - notwithstanding the fact that he can do well there as well, in a leading team he can really excel..
So, given that background one the one hand and the unsatisfying performance on the pitch so far despite the results on the other hand, what can be a possible explanation? I can think of two possible ones, which may be both at work at the same time:
i) He is still experimenting to build the characteristics he wants from the team. That can be a formation/player experimentation which has stopped the last weeks - as people noticed he has stuck with certain people as basic XI lately, but it can also be trying things out on training and waiting to see them happening on the pitch. And that second case can take really long...
I am the last person to be happy to see Rakitic on the pitch, Iniesta a shadow of himself in the basic XI, Suarez in bad shape playing every game, and Roberto, Denis and Paulinho who can at least run on the bench.
But none of us knows what exactly he is working in his trainings. EV is not the type of man that will not try to build a team, but rather manage a squad by using some experienced players to get some results against Malaga here, Getafe there etc
ii) My biggest fear and worry when heard EV will be the new Barca coach has been the fact that he had never coached such a high-calibre club. Some people cannot take the huge stress, responsibility and pressure that accompanies such a job. If that's the case, it is expected that it will be reflected in the way he works, or in the way the team performs. 'Playing safe' regarding formations might be a symptom of the above, which of course goes contrary to the aspiration of building a team with distinctive style play. If you cannot bear the anxiety and the pressure of a draw at home versus minor opponent, you will never be able to build a proper team..
I wish this is not the case, because if it is i cannot see how he can dig himself out of this hole..
I will wait until Christmas and the first Classico to get a more complete picture, before passing any judgment