If they do their jobs properly, good commentators can add a lot of enjoyment to the viewing experience. For starters, they can briefly explain refereeing decisions (bearing in mind that we hope that some viewers are relatively new to the game), they can definitely keep us up to date on replacements, and when a team is down because of a yellow card they can remind us periodically. All these should be standard requirements, but they are often overlooked.
Then it would be good to have a bit of background, and the stories, about some of the lesser known players. The Kiwi and Saffer commentators do that reasonably well. There are some good stories that surround some of our players, and they can and should be told, from time to time.
However, let us lay off the nicknames, particularly as earlier posters have said, the Brendan Cannon syndrome, where every given name ends with an "o" or a "y". It is childish. And could we refer to players occasionally by some term other than "guys"? Perhaps I am just old-fashioned, but the over-use of this Americanism really irks me.
Finally, could Greg Clarke stop calling every player over medium height "big"? As in, the ball comes out to Big Cliffy Palu. Is there a Small Cliffy Palu?
Less is more. Never was this phrase more apposite than when watching the rugby and listening to the commentators on Fox Sports.