My favorites:
Vader, everything, his final scene of those rebel troopers standing there not knowing what was about to happen and you hear vaders breathing and then is light saber come on, I was going crazy when that happened, totally made him the bad a$$ I knew he was in the original trilogy.
Tarkin, I did not read much in the way of spoilers but a day before I read a non spoiler review and it talked about how much screen time Tarkin had and I was interested, and sure enough I was extremely impressed not only with the CGI of him but the over all performance, I did not nit pick it nor was I distracted by the CGI, there were times I really felt it was Peter Cushing, yes looking back it was not perfect but I loved it.
The final battle, Epic is all I will say, nothing wrong with it at all.
Least favorite:
First act was slow, but we had a lot to catch up on, so overall it is a minor complaint.