My experience with ACC (broken achilles full reconstruction, 3 operations in the private system and physio, 80% salary for time off) has only been positive - I know some people have a different experience but IMHO when it works it works really well
When it works sure, but too often the system is adversarial and the behaviour more in line with what you'd see from a private insurer - as opposed to a government entity acting for the good of the people.