Z's offensive game is one of the best overall for all centers in the NBA. he can't run the floor, but not a lot of true centers can really run the floor. He's tall as hell and can block shots and get rebounds. He keeps us in contention as a team. He's experienced.
He just doesn't have that killer instinct, and doesn't have much power/strength. It's harder for a 7 plus footer to be really athletic. how many 7 footers do you see pulling a dunk like LeBron or Vince off?? you don't.
Z will be good until his contract is over, then we just find someone new, or hope he signs for the MLE ,or something small due to his commitment to the Cavs over the years.