1. Poor handling of friend lists - Facebook originally had far more fine-grained controls - you could post on a friend's wall and not have it sent to all your friends, for instance. They tried to bring this back with friend lists, but these are harder to create once you have a high volume of friends.
2. Friend decay - In the real world, friends come and go depending on our location, job, hobbies etc. On Facebook, they stick around forever. Google+ doesn't have a friend decay feature, but benefits from being a "fresh start" for our most recent friend groups.
3. Confusing privacy controls - Sometimes I don't even fully understand Facebook's privacy controls. Google+ is pretty simple - create a group, share only to that group.
4. Facebook groups - In theory these should render Google+ Circles useless, but Facebook groups removes control from the user - I've been added to tons of groups I don't want to be part of and spend a lot of time trying to remove myself.