I think Navi was a valuable asset to
OoT. She was very helpful. The only thing that annoyed me, as with most people, was the fact that she kept nagging you at the begging of the game, telling you how to do certain things. Like in the Deku Tree, for example: Telling you how to open a door? What is that?
But other than that, she was perfectly fine. She gave some interesting info about your enemies. At least with her, I knew what my enemies where called. In WW I had no idea what the names of all the monsters where.
I'm not complaining about the whole game though. Just that one thing.