I'm disappointed his performance this season.
He started well, but then he regressed to last year's Sully.
Three things to consider
-Altho we all have our reservations, it's not over till the fat lady sings. Wait to reach a fuller assessment of Sully later in the season.
-If he continues to play like this, probably the right move will be to trade him, he won't be worth the money he is likely once a protected FA.
-Having said this, if he turns out to be reasonable (and Ainge has his way with players: think of AB's and Crowder's contracts), a renewal might also be an appealing option.
tl;dr: Too early to reach definite conclusions.