Fifteen years is a long time for a conductor to stay with a single orchestra, so it’s not surprising that, as Daniel Barenboim prepares for his final sendoff as music director of the Chicago Symphony this week, the assessments of his tenure are not universally positive. But John von Rhein says that, on balance, Barenboim has been good for the CSO: “Like all marriages, that of Barenboim and the Chicago Symphony survived honeymoon, discord, absences, misunderstandings, threats of divorce and shared successes. Both used the other for their own benefit. Both traveled an enormous learning curve together.”