I don't think Cleary is a great coach. He was average/okay/good prior to getting to Penrith and it is a great system of juniors there that he has done well with.
Bellamy is a great coach. He has done very well with totally different generations of players and also been innovative (in a negative way for the interests of the game unfortunately). Bennett is a great coach, but I am really only saying that because he managed to win at the Dragons. Slingblade, Gump or Langmack could have coached the Broncos and won in the 90s.
Arthur was in that pool of average coaches, his big issue is like the most of rest of them he is a terrible communicator, at least to the fans. If you are going to be a terrible communicator you better get results quick. Ryles is 100% a better communicator to the fans (via the media) than most/many of the other coaches - thus far.
I think Ando was a good coach - I've got him a level above average because of the innovation (mid-season) in 09. He communicated to the fans through that innovation.