It's very hard to rate captaincy from the sidelines.I don't know about that. He was definitely one of the most obviously active captains, in that he tried a lot of funky tactics, which leads to his captaincy being talked about a lot more than someone who used more standard tactics (even if they were better). Whether that makes him a great captain I don't know.
I'd say he's probably one of the best though, but I'm not really basing that on much. It's hard to really rate captaincy from the sidelines.
Tactically it's pretty easy. Hindsight is 20/20. Fleming was great tactically. The funky calls were pretty good in general. The 50/50 calls where any captain could have gone either way he was great at.
Beyond tactics I think you can look at win % compared to quality of resources. His team didn't exactly dominate, but the resources were garbage, and I reckon NZ punched way above their weight. How much of the credit a captain deserves is debatable though.