I think a good angler is:

1) Someone who is cathching fish when no one else is. I am refering to the angler that adapting to conditions, reading the water and thinking "outside of the box", not the angler who just has the right rock that day and got lucky.
2) If you put a good angler on unfamiliar water, they still will produce fish. It is much easier to look good on water that you are intimately familiar with than a foreign place that you have never been.
3) Good sportmanlike etiquette and conduct! Willing to share helpful tips and insight.

Thomas