One Champions League title, 2 League titles including a record winning League title. Strong finances. Rosell has done at least ok. Arguably good or great. You certainly can't say he's done a bad job.
You could argue a case on his reign being distasteful, this includes the dodgy accounting and the zealous campaign to try to discredit the previous regime, maybe even argue the selling of Ibra on the cheap was improper, the selling out of the shirt, the arguments with Cruyff, Pep, not speaking up to defend the club and hiding behind others and so on.