although he's had some very bad calls, he's also had the calls where you wonder how he got it right because everybody else had missed it. He was a diva at times though. What can you expect with the emotional players he had to deal with? Overall, average job. The refs are getting worse than him now so he'd be considered above average in comparison.
Conspiracy theorists can revile him all they want; the fact remains that he was still one of the best officitiators in the league for a while. For those of us who actually watched him, we know he's had such great acuity that he would even make calls that other referees missed at much better vantage points.
His only unacceptable miscalls have been with technical fouls, and therein lies his one major flaw; he acted far too officious when interacting with players and coaches, and he deserves the flak he had for the Tim Duncan debacle. It's really where most of his disreputation stems from, as he was far too emotionally transparent on the job--never a good trait to have as a side-neutral authority figure.
If you can ignore all his tumultuous interactions with players, which many conspiricists don't want to do, he will end up as one of the best officiators in NBA history.